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<div class="section" id="module-difflib">
<h1>7.4. <tt class="xref docutils literal"><span class="pre">difflib</span></tt> — Helpers for computing deltas<a class="headerlink" href="#module-difflib" title="Permalink to this headline">¶</a></h1>
<p class="versionadded">
<span class="versionmodified">New in version 2.1.</span></p>
<p>This module provides classes and functions for comparing sequences. It
can be used for example, for comparing files, and can produce difference
information in various formats, including HTML and context and unified
diffs. For comparing directories and files, see also, the <a title="Compare files efficiently." class="reference external" href="filecmp.html#module-filecmp"><tt class="xref docutils literal"><span class="pre">filecmp</span></tt></a> module.</p>
<dl class="class">
<dt id="difflib.SequenceMatcher">
<em class="property">class </em><tt class="descclassname">difflib.</tt><tt class="descname">SequenceMatcher</tt><a class="headerlink" href="#difflib.SequenceMatcher" title="Permalink to this definition">¶</a></dt>
<dd><p>This is a flexible class for comparing pairs of sequences of any type, so long
as the sequence elements are <a class="reference external" href="../glossary.html#term-hashable"><em class="xref">hashable</em></a>. The basic algorithm predates, and is a
little fancier than, an algorithm published in the late 1980’s by Ratcliff and
Obershelp under the hyperbolic name “gestalt pattern matching.” The idea is to
find the longest contiguous matching subsequence that contains no “junk”
elements (the Ratcliff and Obershelp algorithm doesn’t address junk). The same
idea is then applied recursively to the pieces of the sequences to the left and
to the right of the matching subsequence. This does not yield minimal edit
sequences, but does tend to yield matches that “look right” to people.</p>
<p><strong>Timing:</strong> The basic Ratcliff-Obershelp algorithm is cubic time in the worst
case and quadratic time in the expected case. <a title="difflib.SequenceMatcher" class="reference internal" href="#difflib.SequenceMatcher"><tt class="xref docutils literal"><span class="pre">SequenceMatcher</span></tt></a> is
quadratic time for the worst case and has expected-case behavior dependent in a
complicated way on how many elements the sequences have in common; best case
time is linear.</p>
<p><strong>Heuristic:</strong> To speed-up matching, items that appear more than 1% of the
time in sequences of at least 200 items are treated as junk. This has the
unfortunate side-effect of giving bad results for sequences constructed from
a small set of items. An option to turn off the heuristic will be added to a
future version.</p>
</dd></dl>
<dl class="class">
<dt id="difflib.Differ">
<em class="property">class </em><tt class="descclassname">difflib.</tt><tt class="descname">Differ</tt><a class="headerlink" href="#difflib.Differ" title="Permalink to this definition">¶</a></dt>
<dd><p>This is a class for comparing sequences of lines of text, and producing
human-readable differences or deltas. Differ uses <a title="difflib.SequenceMatcher" class="reference internal" href="#difflib.SequenceMatcher"><tt class="xref docutils literal"><span class="pre">SequenceMatcher</span></tt></a>
both to compare sequences of lines, and to compare sequences of characters
within similar (near-matching) lines.</p>
<p>Each line of a <a title="difflib.Differ" class="reference internal" href="#difflib.Differ"><tt class="xref docutils literal"><span class="pre">Differ</span></tt></a> delta begins with a two-letter code:</p>
<table border="1" class="docutils">
<colgroup>
<col width="19%" />
<col width="81%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Code</th>
<th class="head">Meaning</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">'-</span> <span class="pre">'</span></tt></td>
<td>line unique to sequence 1</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">'+</span> <span class="pre">'</span></tt></td>
<td>line unique to sequence 2</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">'</span> <span class="pre">'</span></tt></td>
<td>line common to both sequences</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">'?</span> <span class="pre">'</span></tt></td>
<td>line not present in either input sequence</td>
</tr>
</tbody>
</table>
<p>Lines beginning with ‘<tt class="docutils literal"><span class="pre">?</span></tt>‘ attempt to guide the eye to intraline differences,
and were not present in either input sequence. These lines can be confusing if
the sequences contain tab characters.</p>
</dd></dl>
<dl class="class">
<dt id="difflib.HtmlDiff">
<em class="property">class </em><tt class="descclassname">difflib.</tt><tt class="descname">HtmlDiff</tt><a class="headerlink" href="#difflib.HtmlDiff" title="Permalink to this definition">¶</a></dt>
<dd><p>This class can be used to create an HTML table (or a complete HTML file
containing the table) showing a side by side, line by line comparison of text
with inter-line and intra-line change highlights. The table can be generated in
either full or contextual difference mode.</p>
<p>The constructor for this class is:</p>
<dl class="function">
<dt id="difflib.HtmlDiff.__init__">
<tt class="descname">__init__</tt><big>(</big><span class="optional">[</span><em>tabsize</em><span class="optional">]</span><span class="optional">[</span>, <em>wrapcolumn</em><span class="optional">]</span><span class="optional">[</span>, <em>linejunk</em><span class="optional">]</span><span class="optional">[</span>, <em>charjunk</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#difflib.HtmlDiff.__init__" title="Permalink to this definition">¶</a></dt>
<dd><p>Initializes instance of <a title="difflib.HtmlDiff" class="reference internal" href="#difflib.HtmlDiff"><tt class="xref docutils literal"><span class="pre">HtmlDiff</span></tt></a>.</p>
<p><em>tabsize</em> is an optional keyword argument to specify tab stop spacing and
defaults to <tt class="docutils literal"><span class="pre">8</span></tt>.</p>
<p><em>wrapcolumn</em> is an optional keyword to specify column number where lines are
broken and wrapped, defaults to <tt class="xref docutils literal"><span class="pre">None</span></tt> where lines are not wrapped.</p>
<p><em>linejunk</em> and <em>charjunk</em> are optional keyword arguments passed into <tt class="docutils literal"><span class="pre">ndiff()</span></tt>
(used by <a title="difflib.HtmlDiff" class="reference internal" href="#difflib.HtmlDiff"><tt class="xref docutils literal"><span class="pre">HtmlDiff</span></tt></a> to generate the side by side HTML differences). See
<tt class="docutils literal"><span class="pre">ndiff()</span></tt> documentation for argument default values and descriptions.</p>
</dd></dl>
<p>The following methods are public:</p>
<dl class="function">
<dt id="difflib.HtmlDiff.make_file">
<tt class="descname">make_file</tt><big>(</big><em>fromlines</em>, <em>tolines</em><span class="optional">[</span>, <em>fromdesc</em><span class="optional">]</span><span class="optional">[</span>, <em>todesc</em><span class="optional">]</span><span class="optional">[</span>, <em>context</em><span class="optional">]</span><span class="optional">[</span>, <em>numlines</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#difflib.HtmlDiff.make_file" title="Permalink to this definition">¶</a></dt>
<dd><p>Compares <em>fromlines</em> and <em>tolines</em> (lists of strings) and returns a string which
is a complete HTML file containing a table showing line by line differences with
inter-line and intra-line changes highlighted.</p>
<p><em>fromdesc</em> and <em>todesc</em> are optional keyword arguments to specify from/to file
column header strings (both default to an empty string).</p>
<p><em>context</em> and <em>numlines</em> are both optional keyword arguments. Set <em>context</em> to
<tt class="xref docutils literal"><span class="pre">True</span></tt> when contextual differences are to be shown, else the default is
<tt class="xref docutils literal"><span class="pre">False</span></tt> to show the full files. <em>numlines</em> defaults to <tt class="docutils literal"><span class="pre">5</span></tt>. When <em>context</em>
is <tt class="xref docutils literal"><span class="pre">True</span></tt> <em>numlines</em> controls the number of context lines which surround the
difference highlights. When <em>context</em> is <tt class="xref docutils literal"><span class="pre">False</span></tt> <em>numlines</em> controls the
number of lines which are shown before a difference highlight when using the
“next” hyperlinks (setting to zero would cause the “next” hyperlinks to place
the next difference highlight at the top of the browser without any leading
context).</p>
</dd></dl>
<dl class="function">
<dt id="difflib.HtmlDiff.make_table">
<tt class="descname">make_table</tt><big>(</big><em>fromlines</em>, <em>tolines</em><span class="optional">[</span>, <em>fromdesc</em><span class="optional">]</span><span class="optional">[</span>, <em>todesc</em><span class="optional">]</span><span class="optional">[</span>, <em>context</em><span class="optional">]</span><span class="optional">[</span>, <em>numlines</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#difflib.HtmlDiff.make_table" title="Permalink to this definition">¶</a></dt>
<dd><p>Compares <em>fromlines</em> and <em>tolines</em> (lists of strings) and returns a string which
is a complete HTML table showing line by line differences with inter-line and
intra-line changes highlighted.</p>
<p>The arguments for this method are the same as those for the <a title="difflib.HtmlDiff.make_file" class="reference internal" href="#difflib.HtmlDiff.make_file"><tt class="xref docutils literal"><span class="pre">make_file()</span></tt></a>
method.</p>
</dd></dl>
<p><tt class="docutils literal"><span class="pre">Tools/scripts/diff.py</span></tt> is a command-line front-end to this class and
contains a good example of its use.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.4.</span></p>
</dd></dl>
<dl class="function">
<dt id="difflib.context_diff">
<tt class="descclassname">difflib.</tt><tt class="descname">context_diff</tt><big>(</big><em>a</em>, <em>b</em><span class="optional">[</span>, <em>fromfile</em><span class="optional">]</span><span class="optional">[</span>, <em>tofile</em><span class="optional">]</span><span class="optional">[</span>, <em>fromfiledate</em><span class="optional">]</span><span class="optional">[</span>, <em>tofiledate</em><span class="optional">]</span><span class="optional">[</span>, <em>n</em><span class="optional">]</span><span class="optional">[</span>, <em>lineterm</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#difflib.context_diff" title="Permalink to this definition">¶</a></dt>
<dd><p>Compare <em>a</em> and <em>b</em> (lists of strings); return a delta (a <a class="reference external" href="../glossary.html#term-generator"><em class="xref">generator</em></a>
generating the delta lines) in context diff format.</p>
<p>Context diffs are a compact way of showing just the lines that have changed plus
a few lines of context. The changes are shown in a before/after style. The
number of context lines is set by <em>n</em> which defaults to three.</p>
<p>By default, the diff control lines (those with <tt class="docutils literal"><span class="pre">***</span></tt> or <tt class="docutils literal"><span class="pre">---</span></tt>) are created
with a trailing newline. This is helpful so that inputs created from
<a title="file.readlines" class="reference external" href="stdtypes.html#file.readlines"><tt class="xref docutils literal"><span class="pre">file.readlines()</span></tt></a> result in diffs that are suitable for use with
<a title="file.writelines" class="reference external" href="stdtypes.html#file.writelines"><tt class="xref docutils literal"><span class="pre">file.writelines()</span></tt></a> since both the inputs and outputs have trailing
newlines.</p>
<p>For inputs that do not have trailing newlines, set the <em>lineterm</em> argument to
<tt class="docutils literal"><span class="pre">""</span></tt> so that the output will be uniformly newline free.</p>
<p>The context diff format normally has a header for filenames and modification
times. Any or all of these may be specified using strings for <em>fromfile</em>,
<em>tofile</em>, <em>fromfiledate</em>, and <em>tofiledate</em>. The modification times are normally
expressed in the format returned by <a title="time.ctime" class="reference external" href="time.html#time.ctime"><tt class="xref docutils literal"><span class="pre">time.ctime()</span></tt></a>. If not specified, the
strings default to blanks.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">s1</span> <span class="o">=</span> <span class="p">[</span><span class="s">'bacon</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'eggs</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'ham</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'guido</span><span class="se">\n</span><span class="s">'</span><span class="p">]</span>
<span class="gp">>>> </span><span class="n">s2</span> <span class="o">=</span> <span class="p">[</span><span class="s">'python</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'eggy</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'hamster</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'guido</span><span class="se">\n</span><span class="s">'</span><span class="p">]</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">context_diff</span><span class="p">(</span><span class="n">s1</span><span class="p">,</span> <span class="n">s2</span><span class="p">,</span> <span class="n">fromfile</span><span class="o">=</span><span class="s">'before.py'</span><span class="p">,</span> <span class="n">tofile</span><span class="o">=</span><span class="s">'after.py'</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">line</span><span class="p">)</span> <span class="c"># doctest: +NORMALIZE_WHITESPACE</span>
<span class="go">*** before.py</span>
<span class="go">--- after.py</span>
<span class="go">***************</span>
<span class="go">*** 1,4 ****</span>
<span class="go">! bacon</span>
<span class="go">! eggs</span>
<span class="go">! ham</span>
<span class="go"> guido</span>
<span class="go">--- 1,4 ----</span>
<span class="go">! python</span>
<span class="go">! eggy</span>
<span class="go">! hamster</span>
<span class="go"> guido</span>
</pre></div>
</div>
<p>See <a class="reference internal" href="#difflib-interface"><em>A command-line interface to difflib</em></a> for a more detailed example.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="function">
<dt id="difflib.get_close_matches">
<tt class="descclassname">difflib.</tt><tt class="descname">get_close_matches</tt><big>(</big><em>word</em>, <em>possibilities</em><span class="optional">[</span>, <em>n</em><span class="optional">]</span><span class="optional">[</span>, <em>cutoff</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#difflib.get_close_matches" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a list of the best “good enough” matches. <em>word</em> is a sequence for which
close matches are desired (typically a string), and <em>possibilities</em> is a list of
sequences against which to match <em>word</em> (typically a list of strings).</p>
<p>Optional argument <em>n</em> (default <tt class="docutils literal"><span class="pre">3</span></tt>) is the maximum number of close matches to
return; <em>n</em> must be greater than <tt class="docutils literal"><span class="pre">0</span></tt>.</p>
<p>Optional argument <em>cutoff</em> (default <tt class="docutils literal"><span class="pre">0.6</span></tt>) is a float in the range [0, 1].
Possibilities that don’t score at least that similar to <em>word</em> are ignored.</p>
<p>The best (no more than <em>n</em>) matches among the possibilities are returned in a
list, sorted by similarity score, most similar first.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">get_close_matches</span><span class="p">(</span><span class="s">'appel'</span><span class="p">,</span> <span class="p">[</span><span class="s">'ape'</span><span class="p">,</span> <span class="s">'apple'</span><span class="p">,</span> <span class="s">'peach'</span><span class="p">,</span> <span class="s">'puppy'</span><span class="p">])</span>
<span class="go">['apple', 'ape']</span>
<span class="gp">>>> </span><span class="kn">import</span> <span class="nn">keyword</span>
<span class="gp">>>> </span><span class="n">get_close_matches</span><span class="p">(</span><span class="s">'wheel'</span><span class="p">,</span> <span class="n">keyword</span><span class="o">.</span><span class="n">kwlist</span><span class="p">)</span>
<span class="go">['while']</span>
<span class="gp">>>> </span><span class="n">get_close_matches</span><span class="p">(</span><span class="s">'apple'</span><span class="p">,</span> <span class="n">keyword</span><span class="o">.</span><span class="n">kwlist</span><span class="p">)</span>
<span class="go">[]</span>
<span class="gp">>>> </span><span class="n">get_close_matches</span><span class="p">(</span><span class="s">'accept'</span><span class="p">,</span> <span class="n">keyword</span><span class="o">.</span><span class="n">kwlist</span><span class="p">)</span>
<span class="go">['except']</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="difflib.ndiff">
<tt class="descclassname">difflib.</tt><tt class="descname">ndiff</tt><big>(</big><em>a</em>, <em>b</em><span class="optional">[</span>, <em>linejunk</em><span class="optional">]</span><span class="optional">[</span>, <em>charjunk</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#difflib.ndiff" title="Permalink to this definition">¶</a></dt>
<dd><p>Compare <em>a</em> and <em>b</em> (lists of strings); return a <a title="difflib.Differ" class="reference internal" href="#difflib.Differ"><tt class="xref docutils literal"><span class="pre">Differ</span></tt></a>-style
delta (a <a class="reference external" href="../glossary.html#term-generator"><em class="xref">generator</em></a> generating the delta lines).</p>
<p>Optional keyword parameters <em>linejunk</em> and <em>charjunk</em> are for filter functions
(or <tt class="xref docutils literal"><span class="pre">None</span></tt>):</p>
<p><em>linejunk</em>: A function that accepts a single string argument, and returns true
if the string is junk, or false if not. The default is (<tt class="xref docutils literal"><span class="pre">None</span></tt>), starting with
Python 2.3. Before then, the default was the module-level function
<a title="difflib.IS_LINE_JUNK" class="reference internal" href="#difflib.IS_LINE_JUNK"><tt class="xref docutils literal"><span class="pre">IS_LINE_JUNK()</span></tt></a>, which filters out lines without visible characters, except
for at most one pound character (<tt class="docutils literal"><span class="pre">'#'</span></tt>). As of Python 2.3, the underlying
<a title="difflib.SequenceMatcher" class="reference internal" href="#difflib.SequenceMatcher"><tt class="xref docutils literal"><span class="pre">SequenceMatcher</span></tt></a> class does a dynamic analysis of which lines are so
frequent as to constitute noise, and this usually works better than the pre-2.3
default.</p>
<p><em>charjunk</em>: A function that accepts a character (a string of length 1), and
returns if the character is junk, or false if not. The default is module-level
function <a title="difflib.IS_CHARACTER_JUNK" class="reference internal" href="#difflib.IS_CHARACTER_JUNK"><tt class="xref docutils literal"><span class="pre">IS_CHARACTER_JUNK()</span></tt></a>, which filters out whitespace characters (a
blank or tab; note: bad idea to include newline in this!).</p>
<p><tt class="docutils literal"><span class="pre">Tools/scripts/ndiff.py</span></tt> is a command-line front-end to this function.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">diff</span> <span class="o">=</span> <span class="n">ndiff</span><span class="p">(</span><span class="s">'one</span><span class="se">\n</span><span class="s">two</span><span class="se">\n</span><span class="s">three</span><span class="se">\n</span><span class="s">'</span><span class="o">.</span><span class="n">splitlines</span><span class="p">(</span><span class="mi">1</span><span class="p">),</span>
<span class="gp">... </span> <span class="s">'ore</span><span class="se">\n</span><span class="s">tree</span><span class="se">\n</span><span class="s">emu</span><span class="se">\n</span><span class="s">'</span><span class="o">.</span><span class="n">splitlines</span><span class="p">(</span><span class="mi">1</span><span class="p">))</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="s">''</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">diff</span><span class="p">),</span>
<span class="go">- one</span>
<span class="go">? ^</span>
<span class="go">+ ore</span>
<span class="go">? ^</span>
<span class="go">- two</span>
<span class="go">- three</span>
<span class="go">? -</span>
<span class="go">+ tree</span>
<span class="go">+ emu</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="difflib.restore">
<tt class="descclassname">difflib.</tt><tt class="descname">restore</tt><big>(</big><em>sequence</em>, <em>which</em><big>)</big><a class="headerlink" href="#difflib.restore" title="Permalink to this definition">¶</a></dt>
<dd><p>Return one of the two sequences that generated a delta.</p>
<p>Given a <em>sequence</em> produced by <a title="difflib.Differ.compare" class="reference internal" href="#difflib.Differ.compare"><tt class="xref docutils literal"><span class="pre">Differ.compare()</span></tt></a> or <a title="difflib.ndiff" class="reference internal" href="#difflib.ndiff"><tt class="xref docutils literal"><span class="pre">ndiff()</span></tt></a>, extract
lines originating from file 1 or 2 (parameter <em>which</em>), stripping off line
prefixes.</p>
<p>Example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">diff</span> <span class="o">=</span> <span class="n">ndiff</span><span class="p">(</span><span class="s">'one</span><span class="se">\n</span><span class="s">two</span><span class="se">\n</span><span class="s">three</span><span class="se">\n</span><span class="s">'</span><span class="o">.</span><span class="n">splitlines</span><span class="p">(</span><span class="mi">1</span><span class="p">),</span>
<span class="gp">... </span> <span class="s">'ore</span><span class="se">\n</span><span class="s">tree</span><span class="se">\n</span><span class="s">emu</span><span class="se">\n</span><span class="s">'</span><span class="o">.</span><span class="n">splitlines</span><span class="p">(</span><span class="mi">1</span><span class="p">))</span>
<span class="gp">>>> </span><span class="n">diff</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">diff</span><span class="p">)</span> <span class="c"># materialize the generated delta into a list</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="s">''</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">restore</span><span class="p">(</span><span class="n">diff</span><span class="p">,</span> <span class="mi">1</span><span class="p">)),</span>
<span class="go">one</span>
<span class="go">two</span>
<span class="go">three</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="s">''</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">restore</span><span class="p">(</span><span class="n">diff</span><span class="p">,</span> <span class="mi">2</span><span class="p">)),</span>
<span class="go">ore</span>
<span class="go">tree</span>
<span class="go">emu</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="difflib.unified_diff">
<tt class="descclassname">difflib.</tt><tt class="descname">unified_diff</tt><big>(</big><em>a</em>, <em>b</em><span class="optional">[</span>, <em>fromfile</em><span class="optional">]</span><span class="optional">[</span>, <em>tofile</em><span class="optional">]</span><span class="optional">[</span>, <em>fromfiledate</em><span class="optional">]</span><span class="optional">[</span>, <em>tofiledate</em><span class="optional">]</span><span class="optional">[</span>, <em>n</em><span class="optional">]</span><span class="optional">[</span>, <em>lineterm</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#difflib.unified_diff" title="Permalink to this definition">¶</a></dt>
<dd><p>Compare <em>a</em> and <em>b</em> (lists of strings); return a delta (a <a class="reference external" href="../glossary.html#term-generator"><em class="xref">generator</em></a>
generating the delta lines) in unified diff format.</p>
<p>Unified diffs are a compact way of showing just the lines that have changed plus
a few lines of context. The changes are shown in a inline style (instead of
separate before/after blocks). The number of context lines is set by <em>n</em> which
defaults to three.</p>
<p>By default, the diff control lines (those with <tt class="docutils literal"><span class="pre">---</span></tt>, <tt class="docutils literal"><span class="pre">+++</span></tt>, or <tt class="docutils literal"><span class="pre">@@</span></tt>) are
created with a trailing newline. This is helpful so that inputs created from
<a title="file.readlines" class="reference external" href="stdtypes.html#file.readlines"><tt class="xref docutils literal"><span class="pre">file.readlines()</span></tt></a> result in diffs that are suitable for use with
<a title="file.writelines" class="reference external" href="stdtypes.html#file.writelines"><tt class="xref docutils literal"><span class="pre">file.writelines()</span></tt></a> since both the inputs and outputs have trailing
newlines.</p>
<p>For inputs that do not have trailing newlines, set the <em>lineterm</em> argument to
<tt class="docutils literal"><span class="pre">""</span></tt> so that the output will be uniformly newline free.</p>
<p>The context diff format normally has a header for filenames and modification
times. Any or all of these may be specified using strings for <em>fromfile</em>,
<em>tofile</em>, <em>fromfiledate</em>, and <em>tofiledate</em>. The modification times are normally
expressed in the format returned by <a title="time.ctime" class="reference external" href="time.html#time.ctime"><tt class="xref docutils literal"><span class="pre">time.ctime()</span></tt></a>. If not specified, the
strings default to blanks.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">s1</span> <span class="o">=</span> <span class="p">[</span><span class="s">'bacon</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'eggs</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'ham</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'guido</span><span class="se">\n</span><span class="s">'</span><span class="p">]</span>
<span class="gp">>>> </span><span class="n">s2</span> <span class="o">=</span> <span class="p">[</span><span class="s">'python</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'eggy</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'hamster</span><span class="se">\n</span><span class="s">'</span><span class="p">,</span> <span class="s">'guido</span><span class="se">\n</span><span class="s">'</span><span class="p">]</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">unified_diff</span><span class="p">(</span><span class="n">s1</span><span class="p">,</span> <span class="n">s2</span><span class="p">,</span> <span class="n">fromfile</span><span class="o">=</span><span class="s">'before.py'</span><span class="p">,</span> <span class="n">tofile</span><span class="o">=</span><span class="s">'after.py'</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">line</span><span class="p">)</span> <span class="c"># doctest: +NORMALIZE_WHITESPACE</span>
<span class="go">--- before.py</span>
<span class="go">+++ after.py</span>
<span class="go">@@ -1,4 +1,4 @@</span>
<span class="go">-bacon</span>
<span class="go">-eggs</span>
<span class="go">-ham</span>
<span class="go">+python</span>
<span class="go">+eggy</span>
<span class="go">+hamster</span>
<span class="go"> guido</span>
</pre></div>
</div>
<p>See <a class="reference internal" href="#difflib-interface"><em>A command-line interface to difflib</em></a> for a more detailed example.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="function">
<dt id="difflib.IS_LINE_JUNK">
<tt class="descclassname">difflib.</tt><tt class="descname">IS_LINE_JUNK</tt><big>(</big><em>line</em><big>)</big><a class="headerlink" href="#difflib.IS_LINE_JUNK" title="Permalink to this definition">¶</a></dt>
<dd>Return true for ignorable lines. The line <em>line</em> is ignorable if <em>line</em> is
blank or contains a single <tt class="docutils literal"><span class="pre">'#'</span></tt>, otherwise it is not ignorable. Used as a
default for parameter <em>linejunk</em> in <a title="difflib.ndiff" class="reference internal" href="#difflib.ndiff"><tt class="xref docutils literal"><span class="pre">ndiff()</span></tt></a> before Python 2.3.</dd></dl>
<dl class="function">
<dt id="difflib.IS_CHARACTER_JUNK">
<tt class="descclassname">difflib.</tt><tt class="descname">IS_CHARACTER_JUNK</tt><big>(</big><em>ch</em><big>)</big><a class="headerlink" href="#difflib.IS_CHARACTER_JUNK" title="Permalink to this definition">¶</a></dt>
<dd>Return true for ignorable characters. The character <em>ch</em> is ignorable if <em>ch</em>
is a space or tab, otherwise it is not ignorable. Used as a default for
parameter <em>charjunk</em> in <a title="difflib.ndiff" class="reference internal" href="#difflib.ndiff"><tt class="xref docutils literal"><span class="pre">ndiff()</span></tt></a>.</dd></dl>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference external" href="http://www.ddj.com/184407970?pgno=5">Pattern Matching: The Gestalt Approach</a></dt>
<dd>Discussion of a similar algorithm by John W. Ratcliff and D. E. Metzener. This
was published in <a class="reference external" href="http://www.ddj.com/">Dr. Dobb’s Journal</a> in July, 1988.</dd>
</dl>
</div>
<div class="section" id="sequencematcher-objects">
<span id="sequence-matcher"></span><h2>7.4.1. SequenceMatcher Objects<a class="headerlink" href="#sequencematcher-objects" title="Permalink to this headline">¶</a></h2>
<p>The <a title="difflib.SequenceMatcher" class="reference internal" href="#difflib.SequenceMatcher"><tt class="xref docutils literal"><span class="pre">SequenceMatcher</span></tt></a> class has this constructor:</p>
<dl class="class">
<dt>
<em class="property">class </em><tt class="descclassname">difflib.</tt><tt class="descname">SequenceMatcher</tt><big>(</big><span class="optional">[</span><em>isjunk</em><span class="optional">[</span>, <em>a</em><span class="optional">[</span>, <em>b</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><big>)</big></dt>
<dd><p>Optional argument <em>isjunk</em> must be <tt class="xref docutils literal"><span class="pre">None</span></tt> (the default) or a one-argument
function that takes a sequence element and returns true if and only if the
element is “junk” and should be ignored. Passing <tt class="xref docutils literal"><span class="pre">None</span></tt> for <em>isjunk</em> is
equivalent to passing <tt class="docutils literal"><span class="pre">lambda</span> <span class="pre">x:</span> <span class="pre">0</span></tt>; in other words, no elements are ignored.
For example, pass:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">lambda</span> <span class="n">x</span><span class="p">:</span> <span class="n">x</span> <span class="ow">in</span> <span class="s">" </span><span class="se">\t</span><span class="s">"</span>
</pre></div>
</div>
<p>if you’re comparing lines as sequences of characters, and don’t want to synch up
on blanks or hard tabs.</p>
<p>The optional arguments <em>a</em> and <em>b</em> are sequences to be compared; both default to
empty strings. The elements of both sequences must be <a class="reference external" href="../glossary.html#term-hashable"><em class="xref">hashable</em></a>.</p>
<p><a title="difflib.SequenceMatcher" class="reference internal" href="#difflib.SequenceMatcher"><tt class="xref docutils literal"><span class="pre">SequenceMatcher</span></tt></a> objects have the following methods:</p>
<dl class="method">
<dt id="difflib.SequenceMatcher.set_seqs">
<tt class="descname">set_seqs</tt><big>(</big><em>a</em>, <em>b</em><big>)</big><a class="headerlink" href="#difflib.SequenceMatcher.set_seqs" title="Permalink to this definition">¶</a></dt>
<dd>Set the two sequences to be compared.</dd></dl>
<p><a title="difflib.SequenceMatcher" class="reference internal" href="#difflib.SequenceMatcher"><tt class="xref docutils literal"><span class="pre">SequenceMatcher</span></tt></a> computes and caches detailed information about the
second sequence, so if you want to compare one sequence against many
sequences, use <a title="difflib.SequenceMatcher.set_seq2" class="reference internal" href="#difflib.SequenceMatcher.set_seq2"><tt class="xref docutils literal"><span class="pre">set_seq2()</span></tt></a> to set the commonly used sequence once and
call <a title="difflib.SequenceMatcher.set_seq1" class="reference internal" href="#difflib.SequenceMatcher.set_seq1"><tt class="xref docutils literal"><span class="pre">set_seq1()</span></tt></a> repeatedly, once for each of the other sequences.</p>
<dl class="method">
<dt id="difflib.SequenceMatcher.set_seq1">
<tt class="descname">set_seq1</tt><big>(</big><em>a</em><big>)</big><a class="headerlink" href="#difflib.SequenceMatcher.set_seq1" title="Permalink to this definition">¶</a></dt>
<dd>Set the first sequence to be compared. The second sequence to be compared
is not changed.</dd></dl>
<dl class="method">
<dt id="difflib.SequenceMatcher.set_seq2">
<tt class="descname">set_seq2</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#difflib.SequenceMatcher.set_seq2" title="Permalink to this definition">¶</a></dt>
<dd>Set the second sequence to be compared. The first sequence to be compared
is not changed.</dd></dl>
<dl class="method">
<dt id="difflib.SequenceMatcher.find_longest_match">
<tt class="descname">find_longest_match</tt><big>(</big><em>alo</em>, <em>ahi</em>, <em>blo</em>, <em>bhi</em><big>)</big><a class="headerlink" href="#difflib.SequenceMatcher.find_longest_match" title="Permalink to this definition">¶</a></dt>
<dd><p>Find longest matching block in <tt class="docutils literal"><span class="pre">a[alo:ahi]</span></tt> and <tt class="docutils literal"><span class="pre">b[blo:bhi]</span></tt>.</p>
<p>If <em>isjunk</em> was omitted or <tt class="xref docutils literal"><span class="pre">None</span></tt>, <a title="difflib.SequenceMatcher.find_longest_match" class="reference internal" href="#difflib.SequenceMatcher.find_longest_match"><tt class="xref docutils literal"><span class="pre">find_longest_match()</span></tt></a> returns
<tt class="docutils literal"><span class="pre">(i,</span> <span class="pre">j,</span> <span class="pre">k)</span></tt> such that <tt class="docutils literal"><span class="pre">a[i:i+k]</span></tt> is equal to <tt class="docutils literal"><span class="pre">b[j:j+k]</span></tt>, where <tt class="docutils literal"><span class="pre">alo</span>
<span class="pre"><=</span> <span class="pre">i</span> <span class="pre"><=</span> <span class="pre">i+k</span> <span class="pre"><=</span> <span class="pre">ahi</span></tt> and <tt class="docutils literal"><span class="pre">blo</span> <span class="pre"><=</span> <span class="pre">j</span> <span class="pre"><=</span> <span class="pre">j+k</span> <span class="pre"><=</span> <span class="pre">bhi</span></tt>. For all <tt class="docutils literal"><span class="pre">(i',</span> <span class="pre">j',</span>
<span class="pre">k')</span></tt> meeting those conditions, the additional conditions <tt class="docutils literal"><span class="pre">k</span> <span class="pre">>=</span> <span class="pre">k'</span></tt>, <tt class="docutils literal"><span class="pre">i</span>
<span class="pre"><=</span> <span class="pre">i'</span></tt>, and if <tt class="docutils literal"><span class="pre">i</span> <span class="pre">==</span> <span class="pre">i'</span></tt>, <tt class="docutils literal"><span class="pre">j</span> <span class="pre"><=</span> <span class="pre">j'</span></tt> are also met. In other words, of
all maximal matching blocks, return one that starts earliest in <em>a</em>, and
of all those maximal matching blocks that start earliest in <em>a</em>, return
the one that starts earliest in <em>b</em>.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="n">SequenceMatcher</span><span class="p">(</span><span class="bp">None</span><span class="p">,</span> <span class="s">" abcd"</span><span class="p">,</span> <span class="s">"abcd abcd"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">s</span><span class="o">.</span><span class="n">find_longest_match</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">9</span><span class="p">)</span>
<span class="go">Match(a=0, b=4, size=5)</span>
</pre></div>
</div>
<p>If <em>isjunk</em> was provided, first the longest matching block is determined
as above, but with the additional restriction that no junk element appears
in the block. Then that block is extended as far as possible by matching
(only) junk elements on both sides. So the resulting block never matches
on junk except as identical junk happens to be adjacent to an interesting
match.</p>
<p>Here’s the same example as before, but considering blanks to be junk. That
prevents <tt class="docutils literal"><span class="pre">'</span> <span class="pre">abcd'</span></tt> from matching the <tt class="docutils literal"><span class="pre">'</span> <span class="pre">abcd'</span></tt> at the tail end of the
second sequence directly. Instead only the <tt class="docutils literal"><span class="pre">'abcd'</span></tt> can match, and
matches the leftmost <tt class="docutils literal"><span class="pre">'abcd'</span></tt> in the second sequence:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="n">SequenceMatcher</span><span class="p">(</span><span class="k">lambda</span> <span class="n">x</span><span class="p">:</span> <span class="n">x</span><span class="o">==</span><span class="s">" "</span><span class="p">,</span> <span class="s">" abcd"</span><span class="p">,</span> <span class="s">"abcd abcd"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">s</span><span class="o">.</span><span class="n">find_longest_match</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">9</span><span class="p">)</span>
<span class="go">Match(a=1, b=0, size=4)</span>
</pre></div>
</div>
<p>If no blocks match, this returns <tt class="docutils literal"><span class="pre">(alo,</span> <span class="pre">blo,</span> <span class="pre">0)</span></tt>.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.6: </span>This method returns a <a class="reference external" href="../glossary.html#term-named-tuple"><em class="xref">named tuple</em></a> <tt class="docutils literal"><span class="pre">Match(a,</span> <span class="pre">b,</span> <span class="pre">size)</span></tt>.</p>
</dd></dl>
<dl class="method">
<dt id="difflib.SequenceMatcher.get_matching_blocks">
<tt class="descname">get_matching_blocks</tt><big>(</big><big>)</big><a class="headerlink" href="#difflib.SequenceMatcher.get_matching_blocks" title="Permalink to this definition">¶</a></dt>
<dd><p>Return list of triples describing matching subsequences. Each triple is of
the form <tt class="docutils literal"><span class="pre">(i,</span> <span class="pre">j,</span> <span class="pre">n)</span></tt>, and means that <tt class="docutils literal"><span class="pre">a[i:i+n]</span> <span class="pre">==</span> <span class="pre">b[j:j+n]</span></tt>. The
triples are monotonically increasing in <em>i</em> and <em>j</em>.</p>
<p>The last triple is a dummy, and has the value <tt class="docutils literal"><span class="pre">(len(a),</span> <span class="pre">len(b),</span> <span class="pre">0)</span></tt>. It
is the only triple with <tt class="docutils literal"><span class="pre">n</span> <span class="pre">==</span> <span class="pre">0</span></tt>. If <tt class="docutils literal"><span class="pre">(i,</span> <span class="pre">j,</span> <span class="pre">n)</span></tt> and <tt class="docutils literal"><span class="pre">(i',</span> <span class="pre">j',</span> <span class="pre">n')</span></tt>
are adjacent triples in the list, and the second is not the last triple in
the list, then <tt class="docutils literal"><span class="pre">i+n</span> <span class="pre">!=</span> <span class="pre">i'</span></tt> or <tt class="docutils literal"><span class="pre">j+n</span> <span class="pre">!=</span> <span class="pre">j'</span></tt>; in other words, adjacent
triples always describe non-adjacent equal blocks.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.5: </span>The guarantee that adjacent triples always describe non-adjacent blocks
was implemented.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="n">SequenceMatcher</span><span class="p">(</span><span class="bp">None</span><span class="p">,</span> <span class="s">"abxcd"</span><span class="p">,</span> <span class="s">"abcd"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">s</span><span class="o">.</span><span class="n">get_matching_blocks</span><span class="p">()</span>
<span class="go">[Match(a=0, b=0, size=2), Match(a=3, b=2, size=2), Match(a=5, b=4, size=0)]</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="difflib.SequenceMatcher.get_opcodes">
<tt class="descname">get_opcodes</tt><big>(</big><big>)</big><a class="headerlink" href="#difflib.SequenceMatcher.get_opcodes" title="Permalink to this definition">¶</a></dt>
<dd><p>Return list of 5-tuples describing how to turn <em>a</em> into <em>b</em>. Each tuple is
of the form <tt class="docutils literal"><span class="pre">(tag,</span> <span class="pre">i1,</span> <span class="pre">i2,</span> <span class="pre">j1,</span> <span class="pre">j2)</span></tt>. The first tuple has <tt class="docutils literal"><span class="pre">i1</span> <span class="pre">==</span> <span class="pre">j1</span> <span class="pre">==</span>
<span class="pre">0</span></tt>, and remaining tuples have <em>i1</em> equal to the <em>i2</em> from the preceding
tuple, and, likewise, <em>j1</em> equal to the previous <em>j2</em>.</p>
<p>The <em>tag</em> values are strings, with these meanings:</p>
<table border="1" class="docutils">
<colgroup>
<col width="25%" />
<col width="75%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Value</th>
<th class="head">Meaning</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">'replace'</span></tt></td>
<td><tt class="docutils literal"><span class="pre">a[i1:i2]</span></tt> should be replaced by
<tt class="docutils literal"><span class="pre">b[j1:j2]</span></tt>.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">'delete'</span></tt></td>
<td><tt class="docutils literal"><span class="pre">a[i1:i2]</span></tt> should be deleted. Note that
<tt class="docutils literal"><span class="pre">j1</span> <span class="pre">==</span> <span class="pre">j2</span></tt> in this case.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">'insert'</span></tt></td>
<td><tt class="docutils literal"><span class="pre">b[j1:j2]</span></tt> should be inserted at
<tt class="docutils literal"><span class="pre">a[i1:i1]</span></tt>. Note that <tt class="docutils literal"><span class="pre">i1</span> <span class="pre">==</span> <span class="pre">i2</span></tt> in
this case.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">'equal'</span></tt></td>
<td><tt class="docutils literal"><span class="pre">a[i1:i2]</span> <span class="pre">==</span> <span class="pre">b[j1:j2]</span></tt> (the sub-sequences
are equal).</td>
</tr>
</tbody>
</table>
<p>For example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a</span> <span class="o">=</span> <span class="s">"qabxcd"</span>
<span class="gp">>>> </span><span class="n">b</span> <span class="o">=</span> <span class="s">"abycdf"</span>
<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="n">SequenceMatcher</span><span class="p">(</span><span class="bp">None</span><span class="p">,</span> <span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">tag</span><span class="p">,</span> <span class="n">i1</span><span class="p">,</span> <span class="n">i2</span><span class="p">,</span> <span class="n">j1</span><span class="p">,</span> <span class="n">j2</span> <span class="ow">in</span> <span class="n">s</span><span class="o">.</span><span class="n">get_opcodes</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">print</span> <span class="p">(</span><span class="s">"</span><span class="si">%7s</span><span class="s"> a[</span><span class="si">%d</span><span class="s">:</span><span class="si">%d</span><span class="s">] (</span><span class="si">%s</span><span class="s">) b[</span><span class="si">%d</span><span class="s">:</span><span class="si">%d</span><span class="s">] (</span><span class="si">%s</span><span class="s">)"</span> <span class="o">%</span>
<span class="gp">... </span> <span class="p">(</span><span class="n">tag</span><span class="p">,</span> <span class="n">i1</span><span class="p">,</span> <span class="n">i2</span><span class="p">,</span> <span class="n">a</span><span class="p">[</span><span class="n">i1</span><span class="p">:</span><span class="n">i2</span><span class="p">],</span> <span class="n">j1</span><span class="p">,</span> <span class="n">j2</span><span class="p">,</span> <span class="n">b</span><span class="p">[</span><span class="n">j1</span><span class="p">:</span><span class="n">j2</span><span class="p">]))</span>
<span class="go"> delete a[0:1] (q) b[0:0] ()</span>
<span class="go"> equal a[1:3] (ab) b[0:2] (ab)</span>
<span class="go">replace a[3:4] (x) b[2:3] (y)</span>
<span class="go"> equal a[4:6] (cd) b[3:5] (cd)</span>
<span class="go"> insert a[6:6] () b[5:6] (f)</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="difflib.SequenceMatcher.get_grouped_opcodes">
<tt class="descname">get_grouped_opcodes</tt><big>(</big><span class="optional">[</span><em>n</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#difflib.SequenceMatcher.get_grouped_opcodes" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a <a class="reference external" href="../glossary.html#term-generator"><em class="xref">generator</em></a> of groups with up to <em>n</em> lines of context.</p>
<p>Starting with the groups returned by <a title="difflib.SequenceMatcher.get_opcodes" class="reference internal" href="#difflib.SequenceMatcher.get_opcodes"><tt class="xref docutils literal"><span class="pre">get_opcodes()</span></tt></a>, this method
splits out smaller change clusters and eliminates intervening ranges which
have no changes.</p>
<p>The groups are returned in the same format as <a title="difflib.SequenceMatcher.get_opcodes" class="reference internal" href="#difflib.SequenceMatcher.get_opcodes"><tt class="xref docutils literal"><span class="pre">get_opcodes()</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="method">
<dt id="difflib.SequenceMatcher.ratio">
<tt class="descname">ratio</tt><big>(</big><big>)</big><a class="headerlink" href="#difflib.SequenceMatcher.ratio" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a measure of the sequences’ similarity as a float in the range [0,
1].</p>
<p>Where T is the total number of elements in both sequences, and M is the
number of matches, this is 2.0*M / T. Note that this is <tt class="docutils literal"><span class="pre">1.0</span></tt> if the
sequences are identical, and <tt class="docutils literal"><span class="pre">0.0</span></tt> if they have nothing in common.</p>
<p>This is expensive to compute if <a title="difflib.SequenceMatcher.get_matching_blocks" class="reference internal" href="#difflib.SequenceMatcher.get_matching_blocks"><tt class="xref docutils literal"><span class="pre">get_matching_blocks()</span></tt></a> or
<a title="difflib.SequenceMatcher.get_opcodes" class="reference internal" href="#difflib.SequenceMatcher.get_opcodes"><tt class="xref docutils literal"><span class="pre">get_opcodes()</span></tt></a> hasn’t already been called, in which case you may want
to try <a title="difflib.SequenceMatcher.quick_ratio" class="reference internal" href="#difflib.SequenceMatcher.quick_ratio"><tt class="xref docutils literal"><span class="pre">quick_ratio()</span></tt></a> or <a title="difflib.SequenceMatcher.real_quick_ratio" class="reference internal" href="#difflib.SequenceMatcher.real_quick_ratio"><tt class="xref docutils literal"><span class="pre">real_quick_ratio()</span></tt></a> first to get an
upper bound.</p>
</dd></dl>
<dl class="method">
<dt id="difflib.SequenceMatcher.quick_ratio">
<tt class="descname">quick_ratio</tt><big>(</big><big>)</big><a class="headerlink" href="#difflib.SequenceMatcher.quick_ratio" title="Permalink to this definition">¶</a></dt>
<dd><p>Return an upper bound on <a title="difflib.SequenceMatcher.ratio" class="reference internal" href="#difflib.SequenceMatcher.ratio"><tt class="xref docutils literal"><span class="pre">ratio()</span></tt></a> relatively quickly.</p>
<p>This isn’t defined beyond that it is an upper bound on <a title="difflib.SequenceMatcher.ratio" class="reference internal" href="#difflib.SequenceMatcher.ratio"><tt class="xref docutils literal"><span class="pre">ratio()</span></tt></a>, and
is faster to compute.</p>
</dd></dl>
<dl class="method">
<dt id="difflib.SequenceMatcher.real_quick_ratio">
<tt class="descname">real_quick_ratio</tt><big>(</big><big>)</big><a class="headerlink" href="#difflib.SequenceMatcher.real_quick_ratio" title="Permalink to this definition">¶</a></dt>
<dd><p>Return an upper bound on <a title="difflib.SequenceMatcher.ratio" class="reference internal" href="#difflib.SequenceMatcher.ratio"><tt class="xref docutils literal"><span class="pre">ratio()</span></tt></a> very quickly.</p>
<p>This isn’t defined beyond that it is an upper bound on <a title="difflib.SequenceMatcher.ratio" class="reference internal" href="#difflib.SequenceMatcher.ratio"><tt class="xref docutils literal"><span class="pre">ratio()</span></tt></a>, and
is faster to compute than either <a title="difflib.SequenceMatcher.ratio" class="reference internal" href="#difflib.SequenceMatcher.ratio"><tt class="xref docutils literal"><span class="pre">ratio()</span></tt></a> or <a title="difflib.SequenceMatcher.quick_ratio" class="reference internal" href="#difflib.SequenceMatcher.quick_ratio"><tt class="xref docutils literal"><span class="pre">quick_ratio()</span></tt></a>.</p>
</dd></dl>
</dd></dl>
<p>The three methods that return the ratio of matching to total characters can give
different results due to differing levels of approximation, although
<tt class="xref docutils literal"><span class="pre">quick_ratio()</span></tt> and <tt class="xref docutils literal"><span class="pre">real_quick_ratio()</span></tt> are always at least as large as
<tt class="xref docutils literal"><span class="pre">ratio()</span></tt>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="n">SequenceMatcher</span><span class="p">(</span><span class="bp">None</span><span class="p">,</span> <span class="s">"abcd"</span><span class="p">,</span> <span class="s">"bcde"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">s</span><span class="o">.</span><span class="n">ratio</span><span class="p">()</span>
<span class="go">0.75</span>
<span class="gp">>>> </span><span class="n">s</span><span class="o">.</span><span class="n">quick_ratio</span><span class="p">()</span>
<span class="go">0.75</span>
<span class="gp">>>> </span><span class="n">s</span><span class="o">.</span><span class="n">real_quick_ratio</span><span class="p">()</span>
<span class="go">1.0</span>
</pre></div>
</div>
</div>
<div class="section" id="sequencematcher-examples">
<span id="id1"></span><h2>7.4.2. SequenceMatcher Examples<a class="headerlink" href="#sequencematcher-examples" title="Permalink to this headline">¶</a></h2>
<p>This example compares two strings, considering blanks to be “junk:”</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="n">SequenceMatcher</span><span class="p">(</span><span class="k">lambda</span> <span class="n">x</span><span class="p">:</span> <span class="n">x</span> <span class="o">==</span> <span class="s">" "</span><span class="p">,</span>
<span class="gp">... </span> <span class="s">"private Thread currentThread;"</span><span class="p">,</span>
<span class="gp">... </span> <span class="s">"private volatile Thread currentThread;"</span><span class="p">)</span>
</pre></div>
</div>
<p><tt class="xref docutils literal"><span class="pre">ratio()</span></tt> returns a float in [0, 1], measuring the similarity of the
sequences. As a rule of thumb, a <tt class="xref docutils literal"><span class="pre">ratio()</span></tt> value over 0.6 means the
sequences are close matches:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">print</span> <span class="nb">round</span><span class="p">(</span><span class="n">s</span><span class="o">.</span><span class="n">ratio</span><span class="p">(),</span> <span class="mi">3</span><span class="p">)</span>
<span class="go">0.866</span>
</pre></div>
</div>
<p>If you’re only interested in where the sequences match,
<tt class="xref docutils literal"><span class="pre">get_matching_blocks()</span></tt> is handy:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">for</span> <span class="n">block</span> <span class="ow">in</span> <span class="n">s</span><span class="o">.</span><span class="n">get_matching_blocks</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">print</span> <span class="s">"a[</span><span class="si">%d</span><span class="s">] and b[</span><span class="si">%d</span><span class="s">] match for </span><span class="si">%d</span><span class="s"> elements"</span> <span class="o">%</span> <span class="n">block</span>
<span class="go">a[0] and b[0] match for 8 elements</span>
<span class="go">a[8] and b[17] match for 21 elements</span>
<span class="go">a[29] and b[38] match for 0 elements</span>
</pre></div>
</div>
<p>Note that the last tuple returned by <tt class="xref docutils literal"><span class="pre">get_matching_blocks()</span></tt> is always a
dummy, <tt class="docutils literal"><span class="pre">(len(a),</span> <span class="pre">len(b),</span> <span class="pre">0)</span></tt>, and this is the only case in which the last
tuple element (number of elements matched) is <tt class="docutils literal"><span class="pre">0</span></tt>.</p>
<p>If you want to know how to change the first sequence into the second, use
<tt class="xref docutils literal"><span class="pre">get_opcodes()</span></tt>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">for</span> <span class="n">opcode</span> <span class="ow">in</span> <span class="n">s</span><span class="o">.</span><span class="n">get_opcodes</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">print</span> <span class="s">"</span><span class="si">%6s</span><span class="s"> a[</span><span class="si">%d</span><span class="s">:</span><span class="si">%d</span><span class="s">] b[</span><span class="si">%d</span><span class="s">:</span><span class="si">%d</span><span class="s">]"</span> <span class="o">%</span> <span class="n">opcode</span>
<span class="go"> equal a[0:8] b[0:8]</span>
<span class="go">insert a[8:8] b[8:17]</span>
<span class="go"> equal a[8:29] b[17:38]</span>
</pre></div>
</div>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<ul class="last simple">
<li>The <a title="difflib.get_close_matches" class="reference internal" href="#difflib.get_close_matches"><tt class="xref docutils literal"><span class="pre">get_close_matches()</span></tt></a> function in this module which shows how
simple code building on <a title="difflib.SequenceMatcher" class="reference internal" href="#difflib.SequenceMatcher"><tt class="xref docutils literal"><span class="pre">SequenceMatcher</span></tt></a> can be used to do useful
work.</li>
<li><a class="reference external" href="http://code.activestate.com/recipes/576729/">Simple version control recipe</a> for a small application
built with <a title="difflib.SequenceMatcher" class="reference internal" href="#difflib.SequenceMatcher"><tt class="xref docutils literal"><span class="pre">SequenceMatcher</span></tt></a>.</li>
</ul>
</div>
</div>
<div class="section" id="differ-objects">
<span id="id2"></span><h2>7.4.3. Differ Objects<a class="headerlink" href="#differ-objects" title="Permalink to this headline">¶</a></h2>
<p>Note that <a title="difflib.Differ" class="reference internal" href="#difflib.Differ"><tt class="xref docutils literal"><span class="pre">Differ</span></tt></a>-generated deltas make no claim to be <strong>minimal</strong>
diffs. To the contrary, minimal diffs are often counter-intuitive, because they
synch up anywhere possible, sometimes accidental matches 100 pages apart.
Restricting synch points to contiguous matches preserves some notion of
locality, at the occasional cost of producing a longer diff.</p>
<p>The <a title="difflib.Differ" class="reference internal" href="#difflib.Differ"><tt class="xref docutils literal"><span class="pre">Differ</span></tt></a> class has this constructor:</p>
<dl class="class">
<dt>
<em class="property">class </em><tt class="descclassname">difflib.</tt><tt class="descname">Differ</tt><big>(</big><span class="optional">[</span><em>linejunk</em><span class="optional">[</span>, <em>charjunk</em><span class="optional">]</span><span class="optional">]</span><big>)</big></dt>
<dd><p>Optional keyword parameters <em>linejunk</em> and <em>charjunk</em> are for filter functions
(or <tt class="xref docutils literal"><span class="pre">None</span></tt>):</p>
<p><em>linejunk</em>: A function that accepts a single string argument, and returns true
if the string is junk. The default is <tt class="xref docutils literal"><span class="pre">None</span></tt>, meaning that no line is
considered junk.</p>
<p><em>charjunk</em>: A function that accepts a single character argument (a string of
length 1), and returns true if the character is junk. The default is <tt class="xref docutils literal"><span class="pre">None</span></tt>,
meaning that no character is considered junk.</p>
<p><a title="difflib.Differ" class="reference internal" href="#difflib.Differ"><tt class="xref docutils literal"><span class="pre">Differ</span></tt></a> objects are used (deltas generated) via a single method:</p>
<dl class="method">
<dt id="difflib.Differ.compare">
<tt class="descname">compare</tt><big>(</big><em>a</em>, <em>b</em><big>)</big><a class="headerlink" href="#difflib.Differ.compare" title="Permalink to this definition">¶</a></dt>
<dd><p>Compare two sequences of lines, and generate the delta (a sequence of lines).</p>
<p>Each sequence must contain individual single-line strings ending with newlines.
Such sequences can be obtained from the <tt class="xref docutils literal"><span class="pre">readlines()</span></tt> method of file-like
objects. The delta generated also consists of newline-terminated strings, ready
to be printed as-is via the <tt class="xref docutils literal"><span class="pre">writelines()</span></tt> method of a file-like object.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="differ-example">
<span id="differ-examples"></span><h2>7.4.4. Differ Example<a class="headerlink" href="#differ-example" title="Permalink to this headline">¶</a></h2>
<p>This example compares two texts. First we set up the texts, sequences of
individual single-line strings ending with newlines (such sequences can also be
obtained from the <tt class="xref docutils literal"><span class="pre">readlines()</span></tt> method of file-like objects):</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">text1</span> <span class="o">=</span> <span class="s">''' 1. Beautiful is better than ugly.</span>
<span class="gp">... </span><span class="s"> 2. Explicit is better than implicit.</span>
<span class="gp">... </span><span class="s"> 3. Simple is better than complex.</span>
<span class="gp">... </span><span class="s"> 4. Complex is better than complicated.</span>
<span class="gp">... </span><span class="s">'''</span><span class="o">.</span><span class="n">splitlines</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">text1</span><span class="p">)</span>
<span class="go">4</span>
<span class="gp">>>> </span><span class="n">text1</span><span class="p">[</span><span class="mi">0</span><span class="p">][</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span>
<span class="go">'\n'</span>
<span class="gp">>>> </span><span class="n">text2</span> <span class="o">=</span> <span class="s">''' 1. Beautiful is better than ugly.</span>
<span class="gp">... </span><span class="s"> 3. Simple is better than complex.</span>
<span class="gp">... </span><span class="s"> 4. Complicated is better than complex.</span>
<span class="gp">... </span><span class="s"> 5. Flat is better than nested.</span>
<span class="gp">... </span><span class="s">'''</span><span class="o">.</span><span class="n">splitlines</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
</pre></div>
</div>
<p>Next we instantiate a Differ object:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">d</span> <span class="o">=</span> <span class="n">Differ</span><span class="p">()</span>
</pre></div>
</div>
<p>Note that when instantiating a <a title="difflib.Differ" class="reference internal" href="#difflib.Differ"><tt class="xref docutils literal"><span class="pre">Differ</span></tt></a> object we may pass functions to
filter out line and character “junk.” See the <a title="difflib.Differ" class="reference internal" href="#difflib.Differ"><tt class="xref docutils literal"><span class="pre">Differ()</span></tt></a> constructor for
details.</p>
<p>Finally, we compare the two:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">result</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">d</span><span class="o">.</span><span class="n">compare</span><span class="p">(</span><span class="n">text1</span><span class="p">,</span> <span class="n">text2</span><span class="p">))</span>
</pre></div>
</div>
<p><tt class="docutils literal"><span class="pre">result</span></tt> is a list of strings, so let’s pretty-print it:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">pprint</span> <span class="kn">import</span> <span class="n">pprint</span>
<span class="gp">>>> </span><span class="n">pprint</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
<span class="go">[' 1. Beautiful is better than ugly.\n',</span>
<span class="go"> '- 2. Explicit is better than implicit.\n',</span>
<span class="go"> '- 3. Simple is better than complex.\n',</span>
<span class="go"> '+ 3. Simple is better than complex.\n',</span>
<span class="go"> '? ++\n',</span>
<span class="go"> '- 4. Complex is better than complicated.\n',</span>
<span class="go"> '? ^ ---- ^\n',</span>
<span class="go"> '+ 4. Complicated is better than complex.\n',</span>
<span class="go"> '? ++++ ^ ^\n',</span>
<span class="go"> '+ 5. Flat is better than nested.\n']</span>
</pre></div>
</div>
<p>As a single multi-line string it looks like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">sys</span>
<span class="gp">>>> </span><span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">writelines</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
<span class="go"> 1. Beautiful is better than ugly.</span>
<span class="go">- 2. Explicit is better than implicit.</span>
<span class="go">- 3. Simple is better than complex.</span>
<span class="go">+ 3. Simple is better than complex.</span>
<span class="go">? ++</span>
<span class="go">- 4. Complex is better than complicated.</span>
<span class="go">? ^ ---- ^</span>
<span class="go">+ 4. Complicated is better than complex.</span>
<span class="go">? ++++ ^ ^</span>
<span class="go">+ 5. Flat is better than nested.</span>
</pre></div>
</div>
</div>
<div class="section" id="a-command-line-interface-to-difflib">
<span id="difflib-interface"></span><h2>7.4.5. A command-line interface to difflib<a class="headerlink" href="#a-command-line-interface-to-difflib" title="Permalink to this headline">¶</a></h2>
<p>This example shows how to use difflib to create a <tt class="docutils literal"><span class="pre">diff</span></tt>-like utility.
It is also contained in the Python source distribution, as
<tt class="docutils literal"><span class="pre">Tools/scripts/diff.py</span></tt>.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="sd">""" Command line interface to difflib.py providing diffs in four formats:</span>
<span class="sd">* ndiff: lists every line and highlights interline changes.</span>
<span class="sd">* context: highlights clusters of changes in a before/after format.</span>
<span class="sd">* unified: highlights clusters of changes in an inline format.</span>
<span class="sd">* html: generates side by side comparison with change highlights.</span>
<span class="sd">"""</span>
<span class="kn">import</span> <span class="nn">sys</span><span class="o">,</span> <span class="nn">os</span><span class="o">,</span> <span class="nn">time</span><span class="o">,</span> <span class="nn">difflib</span><span class="o">,</span> <span class="nn">optparse</span>
<span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="c"># Configure the option parser</span>
<span class="n">usage</span> <span class="o">=</span> <span class="s">"usage: %prog [options] fromfile tofile"</span>
<span class="n">parser</span> <span class="o">=</span> <span class="n">optparse</span><span class="o">.</span><span class="n">OptionParser</span><span class="p">(</span><span class="n">usage</span><span class="p">)</span>
<span class="n">parser</span><span class="o">.</span><span class="n">add_option</span><span class="p">(</span><span class="s">"-c"</span><span class="p">,</span> <span class="n">action</span><span class="o">=</span><span class="s">"store_true"</span><span class="p">,</span> <span class="n">default</span><span class="o">=</span><span class="bp">False</span><span class="p">,</span>
<span class="n">help</span><span class="o">=</span><span class="s">'Produce a context format diff (default)'</span><span class="p">)</span>
<span class="n">parser</span><span class="o">.</span><span class="n">add_option</span><span class="p">(</span><span class="s">"-u"</span><span class="p">,</span> <span class="n">action</span><span class="o">=</span><span class="s">"store_true"</span><span class="p">,</span> <span class="n">default</span><span class="o">=</span><span class="bp">False</span><span class="p">,</span>
<span class="n">help</span><span class="o">=</span><span class="s">'Produce a unified format diff'</span><span class="p">)</span>
<span class="n">hlp</span> <span class="o">=</span> <span class="s">'Produce HTML side by side diff (can use -c and -l in conjunction)'</span>
<span class="n">parser</span><span class="o">.</span><span class="n">add_option</span><span class="p">(</span><span class="s">"-m"</span><span class="p">,</span> <span class="n">action</span><span class="o">=</span><span class="s">"store_true"</span><span class="p">,</span> <span class="n">default</span><span class="o">=</span><span class="bp">False</span><span class="p">,</span> <span class="n">help</span><span class="o">=</span><span class="n">hlp</span><span class="p">)</span>
<span class="n">parser</span><span class="o">.</span><span class="n">add_option</span><span class="p">(</span><span class="s">"-n"</span><span class="p">,</span> <span class="n">action</span><span class="o">=</span><span class="s">"store_true"</span><span class="p">,</span> <span class="n">default</span><span class="o">=</span><span class="bp">False</span><span class="p">,</span>
<span class="n">help</span><span class="o">=</span><span class="s">'Produce a ndiff format diff'</span><span class="p">)</span>
<span class="n">parser</span><span class="o">.</span><span class="n">add_option</span><span class="p">(</span><span class="s">"-l"</span><span class="p">,</span> <span class="s">"--lines"</span><span class="p">,</span> <span class="nb">type</span><span class="o">=</span><span class="s">"int"</span><span class="p">,</span> <span class="n">default</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span>
<span class="n">help</span><span class="o">=</span><span class="s">'Set number of context lines (default 3)'</span><span class="p">)</span>
<span class="p">(</span><span class="n">options</span><span class="p">,</span> <span class="n">args</span><span class="p">)</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">parse_args</span><span class="p">()</span>
<span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="n">parser</span><span class="o">.</span><span class="n">print_help</span><span class="p">()</span>
<span class="n">sys</span><span class="o">.</span><span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="o">!=</span> <span class="mi">2</span><span class="p">:</span>
<span class="n">parser</span><span class="o">.</span><span class="n">error</span><span class="p">(</span><span class="s">"need to specify both a fromfile and tofile"</span><span class="p">)</span>
<span class="n">n</span> <span class="o">=</span> <span class="n">options</span><span class="o">.</span><span class="n">lines</span>
<span class="n">fromfile</span><span class="p">,</span> <span class="n">tofile</span> <span class="o">=</span> <span class="n">args</span> <span class="c"># as specified in the usage string</span>
<span class="c"># we're passing these as arguments to the diff function</span>
<span class="n">fromdate</span> <span class="o">=</span> <span class="n">time</span><span class="o">.</span><span class="n">ctime</span><span class="p">(</span><span class="n">os</span><span class="o">.</span><span class="n">stat</span><span class="p">(</span><span class="n">fromfile</span><span class="p">)</span><span class="o">.</span><span class="n">st_mtime</span><span class="p">)</span>
<span class="n">todate</span> <span class="o">=</span> <span class="n">time</span><span class="o">.</span><span class="n">ctime</span><span class="p">(</span><span class="n">os</span><span class="o">.</span><span class="n">stat</span><span class="p">(</span><span class="n">tofile</span><span class="p">)</span><span class="o">.</span><span class="n">st_mtime</span><span class="p">)</span>
<span class="n">fromlines</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">fromfile</span><span class="p">,</span> <span class="s">'U'</span><span class="p">)</span><span class="o">.</span><span class="n">readlines</span><span class="p">()</span>
<span class="n">tolines</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">tofile</span><span class="p">,</span> <span class="s">'U'</span><span class="p">)</span><span class="o">.</span><span class="n">readlines</span><span class="p">()</span>
<span class="k">if</span> <span class="n">options</span><span class="o">.</span><span class="n">u</span><span class="p">:</span>
<span class="n">diff</span> <span class="o">=</span> <span class="n">difflib</span><span class="o">.</span><span class="n">unified_diff</span><span class="p">(</span><span class="n">fromlines</span><span class="p">,</span> <span class="n">tolines</span><span class="p">,</span> <span class="n">fromfile</span><span class="p">,</span> <span class="n">tofile</span><span class="p">,</span>
<span class="n">fromdate</span><span class="p">,</span> <span class="n">todate</span><span class="p">,</span> <span class="n">n</span><span class="o">=</span><span class="n">n</span><span class="p">)</span>
<span class="k">elif</span> <span class="n">options</span><span class="o">.</span><span class="n">n</span><span class="p">:</span>
<span class="n">diff</span> <span class="o">=</span> <span class="n">difflib</span><span class="o">.</span><span class="n">ndiff</span><span class="p">(</span><span class="n">fromlines</span><span class="p">,</span> <span class="n">tolines</span><span class="p">)</span>
<span class="k">elif</span> <span class="n">options</span><span class="o">.</span><span class="n">m</span><span class="p">:</span>
<span class="n">diff</span> <span class="o">=</span> <span class="n">difflib</span><span class="o">.</span><span class="n">HtmlDiff</span><span class="p">()</span><span class="o">.</span><span class="n">make_file</span><span class="p">(</span><span class="n">fromlines</span><span class="p">,</span> <span class="n">tolines</span><span class="p">,</span> <span class="n">fromfile</span><span class="p">,</span>
<span class="n">tofile</span><span class="p">,</span> <span class="n">context</span><span class="o">=</span><span class="n">options</span><span class="o">.</span><span class="n">c</span><span class="p">,</span>
<span class="n">numlines</span><span class="o">=</span><span class="n">n</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">diff</span> <span class="o">=</span> <span class="n">difflib</span><span class="o">.</span><span class="n">context_diff</span><span class="p">(</span><span class="n">fromlines</span><span class="p">,</span> <span class="n">tolines</span><span class="p">,</span> <span class="n">fromfile</span><span class="p">,</span> <span class="n">tofile</span><span class="p">,</span>
<span class="n">fromdate</span><span class="p">,</span> <span class="n">todate</span><span class="p">,</span> <span class="n">n</span><span class="o">=</span><span class="n">n</span><span class="p">)</span>
<span class="c"># we're using writelines because diff is a generator</span>
<span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">writelines</span><span class="p">(</span><span class="n">diff</span><span class="p">)</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">'__main__'</span><span class="p">:</span>
<span class="n">main</span><span class="p">()</span>
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<li><a class="reference external" href="#">7.4. <tt class="docutils literal"><span class="pre">difflib</span></tt> — Helpers for computing deltas</a><ul>
<li><a class="reference external" href="#sequencematcher-objects">7.4.1. SequenceMatcher Objects</a></li>
<li><a class="reference external" href="#sequencematcher-examples">7.4.2. SequenceMatcher Examples</a></li>
<li><a class="reference external" href="#differ-objects">7.4.3. Differ Objects</a></li>
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