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 <div class="section" id="module-difflib">
<h1>6.3. <a class="reference internal" href="#module-difflib" title="difflib: Helpers for computing differences between objects."><code class="xref py py-mod docutils literal notranslate">difflib</code></a> — Helpers for computing deltas<a class="headerlink" href="#module-difflib" title="Permalink to this headline">¶</a></h1>
Source code: <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/difflib.py">Lib/difflib.py</a>
<hr class="docutils" />
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 class="reference internal" href="filecmp.html#module-filecmp" title="filecmp: Compare files efficiently."><code class="xref py py-mod docutils literal notranslate">filecmp</code></a> module.
<dl class="class">
<dt id="difflib.SequenceMatcher">
class <code class="descclassname">difflib.</code><code class="descname">SequenceMatcher</code><a class="headerlink" href="#difflib.SequenceMatcher" title="Permalink to this definition">¶</a></dt>
<dd>This is a flexible class for comparing pairs of sequences of any type, so long
as the sequence elements are <a class="reference internal" href="../glossary.html#term-hashable">hashable</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; these “junk” elements are ones that are uninteresting in some
sense, such as blank lines or whitespace. (Handling junk is an
extension to the Ratcliff and Obershelp algorithm.) 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.
Timing: The basic Ratcliff-Obershelp algorithm is cubic time in the worst
case and quadratic time in the expected case. <a class="reference internal" href="#difflib.SequenceMatcher" title="difflib.SequenceMatcher"><code class="xref py py-class docutils literal notranslate">SequenceMatcher</code></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.
Automatic junk heuristic: <a class="reference internal" href="#difflib.SequenceMatcher" title="difflib.SequenceMatcher"><code class="xref py py-class docutils literal notranslate">SequenceMatcher</code></a> supports a heuristic that
automatically treats certain sequence items as junk. The heuristic counts how many
times each individual item appears in the sequence. If an item’s duplicates (after
the first one) account for more than 1% of the sequence and the sequence is at least
200 items long, this item is marked as “popular” and is treated as junk for
the purpose of sequence matching. This heuristic can be turned off by setting
the <code class="docutils literal notranslate">autojunk</code> argument to <code class="docutils literal notranslate">False</code> when creating the <a class="reference internal" href="#difflib.SequenceMatcher" title="difflib.SequenceMatcher"><code class="xref py py-class docutils literal notranslate">SequenceMatcher</code></a>.
<div class="versionadded">
New in version 3.2: The autojunk parameter.
</div>
</dd></dl>

<dl class="class">
<dt id="difflib.Differ">
class <code class="descclassname">difflib.</code><code class="descname">Differ</code><a class="headerlink" href="#difflib.Differ" title="Permalink to this definition">¶</a></dt>
<dd>This is a class for comparing sequences of lines of text, and producing
human-readable differences or deltas. Differ uses <a class="reference internal" href="#difflib.SequenceMatcher" title="difflib.SequenceMatcher"><code class="xref py py-class docutils literal notranslate">SequenceMatcher</code></a>
both to compare sequences of lines, and to compare sequences of characters
within similar (near-matching) lines.
Each line of a <a class="reference internal" href="#difflib.Differ" title="difflib.Differ"><code class="xref py py-class docutils literal notranslate">Differ</code></a> delta begins with a two-letter code:
<table border="1" class="docutils">
<colgroup>
<col width="19%" />
<col width="81%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Code</th>
<th class="head">Meaning</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal notranslate">'- '</code></td>
<td>line unique to sequence 1</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">'+ '</code></td>
<td>line unique to sequence 2</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">'&#160; '</code></td>
<td>line common to both sequences</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">'? '</code></td>
<td>line not present in either input sequence</td>
</tr>
</tbody>
</table>
Lines beginning with ‘<code class="docutils literal notranslate">?</code>’ 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.
</dd></dl>

<dl class="class">
<dt id="difflib.HtmlDiff">
class <code class="descclassname">difflib.</code><code class="descname">HtmlDiff</code><a class="headerlink" href="#difflib.HtmlDiff" title="Permalink to this definition">¶</a></dt>
<dd>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.
The constructor for this class is:
<dl class="method">
<dt id="difflib.HtmlDiff.__init__">
<code class="descname">__init__</code>(tabsize=8, wrapcolumn=None, linejunk=None, charjunk=IS_CHARACTER_JUNK)<a class="headerlink" href="#difflib.HtmlDiff.__init__" title="Permalink to this definition">¶</a></dt>
<dd>Initializes instance of <a class="reference internal" href="#difflib.HtmlDiff" title="difflib.HtmlDiff"><code class="xref py py-class docutils literal notranslate">HtmlDiff</code></a>.
tabsize is an optional keyword argument to specify tab stop spacing and
defaults to <code class="docutils literal notranslate">8</code>.
wrapcolumn is an optional keyword to specify column number where lines are
broken and wrapped, defaults to <code class="docutils literal notranslate">None</code> where lines are not wrapped.
linejunk and charjunk are optional keyword arguments passed into <a class="reference internal" href="#difflib.ndiff" title="difflib.ndiff"><code class="xref py py-func docutils literal notranslate">ndiff()</code></a>
(used by <a class="reference internal" href="#difflib.HtmlDiff" title="difflib.HtmlDiff"><code class="xref py py-class docutils literal notranslate">HtmlDiff</code></a> to generate the side by side HTML differences). See
<a class="reference internal" href="#difflib.ndiff" title="difflib.ndiff"><code class="xref py py-func docutils literal notranslate">ndiff()</code></a> documentation for argument default values and descriptions.
</dd></dl>

The following methods are public:
<dl class="method">
<dt id="difflib.HtmlDiff.make_file">
<code class="descname">make_file</code>(fromlines, tolines, fromdesc='', todesc='', context=False, numlines=5, *, charset='utf-8')<a class="headerlink" href="#difflib.HtmlDiff.make_file" title="Permalink to this definition">¶</a></dt>
<dd>Compares fromlines and tolines (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.
fromdesc and todesc are optional keyword arguments to specify from/to file
column header strings (both default to an empty string).
context and numlines are both optional keyword arguments. Set context to
<code class="docutils literal notranslate">True</code> when contextual differences are to be shown, else the default is
<code class="docutils literal notranslate">False</code> to show the full files. numlines defaults to <code class="docutils literal notranslate">5</code>. When context
is <code class="docutils literal notranslate">True</code> numlines controls the number of context lines which surround the
difference highlights. When context is <code class="docutils literal notranslate">False</code> numlines 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).
<div class="versionchanged">
Changed in version 3.5: charset keyword-only argument was added. The default charset of
HTML document changed from <code class="docutils literal notranslate">'ISO-8859-1'</code> to <code class="docutils literal notranslate">'utf-8'</code>.
</div>
</dd></dl>

<dl class="method">
<dt id="difflib.HtmlDiff.make_table">
<code class="descname">make_table</code>(fromlines, tolines, fromdesc='', todesc='', context=False, numlines=5)<a class="headerlink" href="#difflib.HtmlDiff.make_table" title="Permalink to this definition">¶</a></dt>
<dd>Compares fromlines and tolines (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.
The arguments for this method are the same as those for the <a class="reference internal" href="#difflib.HtmlDiff.make_file" title="difflib.HtmlDiff.make_file"><code class="xref py py-meth docutils literal notranslate">make_file()</code></a>
method.
</dd></dl>

<code class="file docutils literal notranslate">Tools/scripts/diff.py</code> is a command-line front-end to this class and
contains a good example of its use.
</dd></dl>

<dl class="function">
<dt id="difflib.context_diff">
<code class="descclassname">difflib.</code><code class="descname">context_diff</code>(a, b, fromfile='', tofile='', fromfiledate='', tofiledate='', n=3, lineterm='\n')<a class="headerlink" href="#difflib.context_diff" title="Permalink to this definition">¶</a></dt>
<dd>Compare a and b (lists of strings); return a delta (a <a class="reference internal" href="../glossary.html#term-generator">generator</a>
generating the delta lines) in context diff format.
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 n which defaults to three.
By default, the diff control lines (those with <code class="docutils literal notranslate">***</code> or <code class="docutils literal notranslate">---</code>) are created
with a trailing newline. This is helpful so that inputs created from
<a class="reference internal" href="io.html#io.IOBase.readlines" title="io.IOBase.readlines"><code class="xref py py-func docutils literal notranslate">io.IOBase.readlines()</code></a> result in diffs that are suitable for use with
<a class="reference internal" href="io.html#io.IOBase.writelines" title="io.IOBase.writelines"><code class="xref py py-func docutils literal notranslate">io.IOBase.writelines()</code></a> since both the inputs and outputs have trailing
newlines.
For inputs that do not have trailing newlines, set the lineterm argument to
<code class="docutils literal notranslate">&quot;&quot;</code> so that the output will be uniformly newline free.
The context diff format normally has a header for filenames and modification
times. Any or all of these may be specified using strings for fromfile,
tofile, fromfiledate, and tofiledate. The modification times are normally
expressed in the ISO 8601 format. If not specified, the
strings default to blanks.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; s1 = [&#39;bacon\n&#39;, &#39;eggs\n&#39;, &#39;ham\n&#39;, &#39;guido\n&#39;]
&gt;&gt;&gt; s2 = [&#39;python\n&#39;, &#39;eggy\n&#39;, &#39;hamster\n&#39;, &#39;guido\n&#39;]
&gt;&gt;&gt; sys.stdout.writelines(context_diff(s1, s2, fromfile=&#39;before.py&#39;, tofile=&#39;after.py&#39;))
*** before.py
--- after.py
***************
*** 1,4 ****
! bacon
! eggs
! ham
 guido
--- 1,4 ----
! python
! eggy
! hamster
 guido
</pre></div>
</div>
See <a class="reference internal" href="#difflib-interface">A command-line interface to difflib</a> for a more detailed example.
</dd></dl>

<dl class="function">
<dt id="difflib.get_close_matches">
<code class="descclassname">difflib.</code><code class="descname">get_close_matches</code>(word, possibilities, n=3, cutoff=0.6)<a class="headerlink" href="#difflib.get_close_matches" title="Permalink to this definition">¶</a></dt>
<dd>Return a list of the best “good enough” matches. word is a sequence for which
close matches are desired (typically a string), and possibilities is a list of
sequences against which to match word (typically a list of strings).
Optional argument n (default <code class="docutils literal notranslate">3</code>) is the maximum number of close matches to
return; n must be greater than <code class="docutils literal notranslate">0</code>.
Optional argument cutoff (default <code class="docutils literal notranslate">0.6</code>) is a float in the range [0, 1].
Possibilities that don’t score at least that similar to word are ignored.
The best (no more than n) matches among the possibilities are returned in a
list, sorted by similarity score, most similar first.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; get_close_matches(&#39;appel&#39;, [&#39;ape&#39;, &#39;apple&#39;, &#39;peach&#39;, &#39;puppy&#39;])
[&#39;apple&#39;, &#39;ape&#39;]
&gt;&gt;&gt; import keyword
&gt;&gt;&gt; get_close_matches(&#39;wheel&#39;, keyword.kwlist)
[&#39;while&#39;]
&gt;&gt;&gt; get_close_matches(&#39;pineapple&#39;, keyword.kwlist)
[]
&gt;&gt;&gt; get_close_matches(&#39;accept&#39;, keyword.kwlist)
[&#39;except&#39;]
</pre></div>
</div>
</dd></dl>

<dl class="function">
<dt id="difflib.ndiff">
<code class="descclassname">difflib.</code><code class="descname">ndiff</code>(a, b, linejunk=None, charjunk=IS_CHARACTER_JUNK)<a class="headerlink" href="#difflib.ndiff" title="Permalink to this definition">¶</a></dt>
<dd>Compare a and b (lists of strings); return a <a class="reference internal" href="#difflib.Differ" title="difflib.Differ"><code class="xref py py-class docutils literal notranslate">Differ</code></a>-style
delta (a <a class="reference internal" href="../glossary.html#term-generator">generator</a> generating the delta lines).
Optional keyword parameters linejunk and charjunk are filtering functions
(or <code class="docutils literal notranslate">None</code>):
linejunk: A function that accepts a single string argument, and returns
true if the string is junk, or false if not. The default is <code class="docutils literal notranslate">None</code>. There
is also a module-level function <a class="reference internal" href="#difflib.IS_LINE_JUNK" title="difflib.IS_LINE_JUNK"><code class="xref py py-func docutils literal notranslate">IS_LINE_JUNK()</code></a>, which filters out lines
without visible characters, except for at most one pound character (<code class="docutils literal notranslate">'#'</code>)
– however the underlying <a class="reference internal" href="#difflib.SequenceMatcher" title="difflib.SequenceMatcher"><code class="xref py py-class docutils literal notranslate">SequenceMatcher</code></a> class does a dynamic
analysis of which lines are so frequent as to constitute noise, and this
usually works better than using this function.
charjunk: 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 class="reference internal" href="#difflib.IS_CHARACTER_JUNK" title="difflib.IS_CHARACTER_JUNK"><code class="xref py py-func docutils literal notranslate">IS_CHARACTER_JUNK()</code></a>, which filters out whitespace characters (a
blank or tab; it’s a bad idea to include newline in this!).
<code class="file docutils literal notranslate">Tools/scripts/ndiff.py</code> is a command-line front-end to this function.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; diff = ndiff(&#39;one\ntwo\nthree\n&#39;.splitlines(keepends=True),
... &#39;ore\ntree\nemu\n&#39;.splitlines(keepends=True))
&gt;&gt;&gt; print(&#39;&#39;.join(diff), end=&quot;&quot;)
- one
? ^
+ ore
? ^
- two
- three
? -
+ tree
+ emu
</pre></div>
</div>
</dd></dl>

<dl class="function">
<dt id="difflib.restore">
<code class="descclassname">difflib.</code><code class="descname">restore</code>(sequence, which)<a class="headerlink" href="#difflib.restore" title="Permalink to this definition">¶</a></dt>
<dd>Return one of the two sequences that generated a delta.
Given a sequence produced by <a class="reference internal" href="#difflib.Differ.compare" title="difflib.Differ.compare"><code class="xref py py-meth docutils literal notranslate">Differ.compare()</code></a> or <a class="reference internal" href="#difflib.ndiff" title="difflib.ndiff"><code class="xref py py-func docutils literal notranslate">ndiff()</code></a>, extract
lines originating from file 1 or 2 (parameter which), stripping off line
prefixes.
Example:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; diff = ndiff(&#39;one\ntwo\nthree\n&#39;.splitlines(keepends=True),
... &#39;ore\ntree\nemu\n&#39;.splitlines(keepends=True))
&gt;&gt;&gt; diff = list(diff) # materialize the generated delta into a list
&gt;&gt;&gt; print(&#39;&#39;.join(restore(diff, 1)), end=&quot;&quot;)
one
two
three
&gt;&gt;&gt; print(&#39;&#39;.join(restore(diff, 2)), end=&quot;&quot;)
ore
tree
emu
</pre></div>
</div>
</dd></dl>

<dl class="function">
<dt id="difflib.unified_diff">
<code class="descclassname">difflib.</code><code class="descname">unified_diff</code>(a, b, fromfile='', tofile='', fromfiledate='', tofiledate='', n=3, lineterm='\n')<a class="headerlink" href="#difflib.unified_diff" title="Permalink to this definition">¶</a></dt>
<dd>Compare a and b (lists of strings); return a delta (a <a class="reference internal" href="../glossary.html#term-generator">generator</a>
generating the delta lines) in unified diff format.
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 an inline style (instead of
separate before/after blocks). The number of context lines is set by n which
defaults to three.
By default, the diff control lines (those with <code class="docutils literal notranslate">---</code>, <code class="docutils literal notranslate">+++</code>, or <code class="docutils literal notranslate">&#64;&#64;</code>) are
created with a trailing newline. This is helpful so that inputs created from
<a class="reference internal" href="io.html#io.IOBase.readlines" title="io.IOBase.readlines"><code class="xref py py-func docutils literal notranslate">io.IOBase.readlines()</code></a> result in diffs that are suitable for use with
<a class="reference internal" href="io.html#io.IOBase.writelines" title="io.IOBase.writelines"><code class="xref py py-func docutils literal notranslate">io.IOBase.writelines()</code></a> since both the inputs and outputs have trailing
newlines.
For inputs that do not have trailing newlines, set the lineterm argument to
<code class="docutils literal notranslate">&quot;&quot;</code> so that the output will be uniformly newline free.
The context diff format normally has a header for filenames and modification
times. Any or all of these may be specified using strings for fromfile,
tofile, fromfiledate, and tofiledate. The modification times are normally
expressed in the ISO 8601 format. If not specified, the
strings default to blanks.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; s1 = [&#39;bacon\n&#39;, &#39;eggs\n&#39;, &#39;ham\n&#39;, &#39;guido\n&#39;]
&gt;&gt;&gt; s2 = [&#39;python\n&#39;, &#39;eggy\n&#39;, &#39;hamster\n&#39;, &#39;guido\n&#39;]
&gt;&gt;&gt; sys.stdout.writelines(unified_diff(s1, s2, fromfile=&#39;before.py&#39;, tofile=&#39;after.py&#39;))
--- before.py
+++ after.py
@@ -1,4 +1,4 @@
-bacon
-eggs
-ham
+python
+eggy
+hamster
 guido
</pre></div>
</div>
See <a class="reference internal" href="#difflib-interface">A command-line interface to difflib</a> for a more detailed example.
</dd></dl>

<dl class="function">
<dt id="difflib.diff_bytes">
<code class="descclassname">difflib.</code><code class="descname">diff_bytes</code>(dfunc, a, b, fromfile=b'', tofile=b'', fromfiledate=b'', tofiledate=b'', n=3, lineterm=b'\n')<a class="headerlink" href="#difflib.diff_bytes" title="Permalink to this definition">¶</a></dt>
<dd>Compare a and b (lists of bytes objects) using dfunc; yield a
sequence of delta lines (also bytes) in the format returned by dfunc.
dfunc must be a callable, typically either <a class="reference internal" href="#difflib.unified_diff" title="difflib.unified_diff"><code class="xref py py-func docutils literal notranslate">unified_diff()</code></a> or
<a class="reference internal" href="#difflib.context_diff" title="difflib.context_diff"><code class="xref py py-func docutils literal notranslate">context_diff()</code></a>.
Allows you to compare data with unknown or inconsistent encoding. All
inputs except n must be bytes objects, not str. Works by losslessly
converting all inputs (except n) to str, and calling <code class="docutils literal notranslate">dfunc(a, b,
fromfile, tofile, fromfiledate, tofiledate, n, lineterm)</code>. The output of
dfunc is then converted back to bytes, so the delta lines that you
receive have the same unknown/inconsistent encodings as a and b.
<div class="versionadded">
New in version 3.5.
</div>
</dd></dl>

<dl class="function">
<dt id="difflib.IS_LINE_JUNK">
<code class="descclassname">difflib.</code><code class="descname">IS_LINE_JUNK</code>(line)<a class="headerlink" href="#difflib.IS_LINE_JUNK" title="Permalink to this definition">¶</a></dt>
<dd>Return true for ignorable lines. The line line is ignorable if line is
blank or contains a single <code class="docutils literal notranslate">'#'</code>, otherwise it is not ignorable. Used as a
default for parameter linejunk in <a class="reference internal" href="#difflib.ndiff" title="difflib.ndiff"><code class="xref py py-func docutils literal notranslate">ndiff()</code></a> in older versions.
</dd></dl>

<dl class="function">
<dt id="difflib.IS_CHARACTER_JUNK">
<code class="descclassname">difflib.</code><code class="descname">IS_CHARACTER_JUNK</code>(ch)<a class="headerlink" href="#difflib.IS_CHARACTER_JUNK" title="Permalink to this definition">¶</a></dt>
<dd>Return true for ignorable characters. The character ch is ignorable if ch
is a space or tab, otherwise it is not ignorable. Used as a default for
parameter charjunk in <a class="reference internal" href="#difflib.ndiff" title="difflib.ndiff"><code class="xref py py-func docutils literal notranslate">ndiff()</code></a>.
</dd></dl>

<div class="admonition seealso">
See also
<dl class="last docutils">
<dt><a class="reference external" href="http://www.drdobbs.com/database/pattern-matching-the-gestalt-approach/184407970">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.drdobbs.com/">Dr. Dobb’s Journal</a> in July, 1988.</dd>
</dl>
</div>
<div class="section" id="sequencematcher-objects">
<h2>6.3.1. SequenceMatcher Objects<a class="headerlink" href="#sequencematcher-objects" title="Permalink to this headline">¶</a></h2>
The <a class="reference internal" href="#difflib.SequenceMatcher" title="difflib.SequenceMatcher"><code class="xref py py-class docutils literal notranslate">SequenceMatcher</code></a> class has this constructor:
<dl class="class">
<dt>
class <code class="descclassname">difflib.</code><code class="descname">SequenceMatcher</code>(isjunk=None, a='', b='', autojunk=True)</dt>
<dd>Optional argument isjunk must be <code class="docutils literal notranslate">None</code> (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 <code class="docutils literal notranslate">None</code> for isjunk is
equivalent to passing <code class="docutils literal notranslate">lambda x: 0</code>; in other words, no elements are ignored.
For example, pass:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>lambda x: x in &quot; \t&quot;
</pre></div>
</div>
if you’re comparing lines as sequences of characters, and don’t want to synch up
on blanks or hard tabs.
The optional arguments a and b are sequences to be compared; both default to
empty strings. The elements of both sequences must be <a class="reference internal" href="../glossary.html#term-hashable">hashable</a>.
The optional argument autojunk can be used to disable the automatic junk
heuristic.
<div class="versionadded">
New in version 3.2: The autojunk parameter.
</div>
SequenceMatcher objects get three data attributes: bjunk is the
set of elements of b for which isjunk is <code class="docutils literal notranslate">True</code>; bpopular is the set of
non-junk elements considered popular by the heuristic (if it is not
disabled); b2j is a dict mapping the remaining elements of b to a list
of positions where they occur. All three are reset whenever b is reset
with <a class="reference internal" href="#difflib.SequenceMatcher.set_seqs" title="difflib.SequenceMatcher.set_seqs"><code class="xref py py-meth docutils literal notranslate">set_seqs()</code></a> or <a class="reference internal" href="#difflib.SequenceMatcher.set_seq2" title="difflib.SequenceMatcher.set_seq2"><code class="xref py py-meth docutils literal notranslate">set_seq2()</code></a>.
<div class="versionadded">
New in version 3.2: The bjunk and bpopular attributes.
</div>
<a class="reference internal" href="#difflib.SequenceMatcher" title="difflib.SequenceMatcher"><code class="xref py py-class docutils literal notranslate">SequenceMatcher</code></a> objects have the following methods:
<dl class="method">
<dt id="difflib.SequenceMatcher.set_seqs">
<code class="descname">set_seqs</code>(a, b)<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>

<a class="reference internal" href="#difflib.SequenceMatcher" title="difflib.SequenceMatcher"><code class="xref py py-class docutils literal notranslate">SequenceMatcher</code></a> computes and caches detailed information about the
second sequence, so if you want to compare one sequence against many
sequences, use <a class="reference internal" href="#difflib.SequenceMatcher.set_seq2" title="difflib.SequenceMatcher.set_seq2"><code class="xref py py-meth docutils literal notranslate">set_seq2()</code></a> to set the commonly used sequence once and
call <a class="reference internal" href="#difflib.SequenceMatcher.set_seq1" title="difflib.SequenceMatcher.set_seq1"><code class="xref py py-meth docutils literal notranslate">set_seq1()</code></a> repeatedly, once for each of the other sequences.
<dl class="method">
<dt id="difflib.SequenceMatcher.set_seq1">
<code class="descname">set_seq1</code>(a)<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">
<code class="descname">set_seq2</code>(b)<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">
<code class="descname">find_longest_match</code>(alo, ahi, blo, bhi)<a class="headerlink" href="#difflib.SequenceMatcher.find_longest_match" title="Permalink to this definition">¶</a></dt>
<dd>Find longest matching block in <code class="docutils literal notranslate">a[alo:ahi]</code> and <code class="docutils literal notranslate">b[blo:bhi]</code>.
If isjunk was omitted or <code class="docutils literal notranslate">None</code>, <a class="reference internal" href="#difflib.SequenceMatcher.find_longest_match" title="difflib.SequenceMatcher.find_longest_match"><code class="xref py py-meth docutils literal notranslate">find_longest_match()</code></a> returns
<code class="docutils literal notranslate">(i, j, k)</code> such that <code class="docutils literal notranslate">a[i:i+k]</code> is equal to <code class="docutils literal notranslate">b[j:j+k]</code>, where <code class="docutils literal notranslate">alo
&lt;= i &lt;= i+k &lt;= ahi</code> and <code class="docutils literal notranslate">blo &lt;= j &lt;= j+k &lt;= bhi</code>. For all <code class="docutils literal notranslate">(i', j',
k')</code> meeting those conditions, the additional conditions <code class="docutils literal notranslate">k &gt;= k'</code>, <code class="docutils literal notranslate">i
&lt;= i'</code>, and if <code class="docutils literal notranslate">i == i'</code>, <code class="docutils literal notranslate">j &lt;= j'</code> are also met. In other words, of
all maximal matching blocks, return one that starts earliest in a, and
of all those maximal matching blocks that start earliest in a, return
the one that starts earliest in b.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; s = SequenceMatcher(None, &quot; abcd&quot;, &quot;abcd abcd&quot;)
&gt;&gt;&gt; s.find_longest_match(0, 5, 0, 9)
Match(a=0, b=4, size=5)
</pre></div>
</div>
If isjunk 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.
Here’s the same example as before, but considering blanks to be junk. That
prevents <code class="docutils literal notranslate">' abcd'</code> from matching the <code class="docutils literal notranslate">' abcd'</code> at the tail end of the
second sequence directly. Instead only the <code class="docutils literal notranslate">'abcd'</code> can match, and
matches the leftmost <code class="docutils literal notranslate">'abcd'</code> in the second sequence:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; s = SequenceMatcher(lambda x: x==&quot; &quot;, &quot; abcd&quot;, &quot;abcd abcd&quot;)
&gt;&gt;&gt; s.find_longest_match(0, 5, 0, 9)
Match(a=1, b=0, size=4)
</pre></div>
</div>
If no blocks match, this returns <code class="docutils literal notranslate">(alo, blo, 0)</code>.
This method returns a <a class="reference internal" href="../glossary.html#term-named-tuple">named tuple</a> <code class="docutils literal notranslate">Match(a, b, size)</code>.
</dd></dl>

<dl class="method">
<dt id="difflib.SequenceMatcher.get_matching_blocks">
<code class="descname">get_matching_blocks</code>()<a class="headerlink" href="#difflib.SequenceMatcher.get_matching_blocks" title="Permalink to this definition">¶</a></dt>
<dd>Return list of triples describing matching subsequences. Each triple is of
the form <code class="docutils literal notranslate">(i, j, n)</code>, and means that <code class="docutils literal notranslate">a[i:i+n] == b[j:j+n]</code>. The
triples are monotonically increasing in i and j.
The last triple is a dummy, and has the value <code class="docutils literal notranslate">(len(a), len(b), 0)</code>. It
is the only triple with <code class="docutils literal notranslate">n == 0</code>. If <code class="docutils literal notranslate">(i, j, n)</code> and <code class="docutils literal notranslate">(i', j', n')</code>
are adjacent triples in the list, and the second is not the last triple in
the list, then <code class="docutils literal notranslate">i+n != i'</code> or <code class="docutils literal notranslate">j+n != j'</code>; in other words, adjacent
triples always describe non-adjacent equal blocks.
<div class="highlight-pycon notranslate"><div class="highlight"><pre>&gt;&gt;&gt; s = SequenceMatcher(None, &quot;abxcd&quot;, &quot;abcd&quot;)
&gt;&gt;&gt; s.get_matching_blocks()
[Match(a=0, b=0, size=2), Match(a=3, b=2, size=2), Match(a=5, b=4, size=0)]
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="difflib.SequenceMatcher.get_opcodes">
<code class="descname">get_opcodes</code>()<a class="headerlink" href="#difflib.SequenceMatcher.get_opcodes" title="Permalink to this definition">¶</a></dt>
<dd>Return list of 5-tuples describing how to turn a into b. Each tuple is
of the form <code class="docutils literal notranslate">(tag, i1, i2, j1, j2)</code>. The first tuple has <code class="docutils literal notranslate">i1 == j1 ==
0</code>, and remaining tuples have i1 equal to the i2 from the preceding
tuple, and, likewise, j1 equal to the previous j2.
The tag values are strings, with these meanings:
<table border="1" class="docutils">
<colgroup>
<col width="25%" />
<col width="75%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Value</th>
<th class="head">Meaning</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal notranslate">'replace'</code></td>
<td><code class="docutils literal notranslate">a[i1:i2]</code> should be replaced by
<code class="docutils literal notranslate">b[j1:j2]</code>.</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">'delete'</code></td>
<td><code class="docutils literal notranslate">a[i1:i2]</code> should be deleted. Note that
<code class="docutils literal notranslate">j1 == j2</code> in this case.</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">'insert'</code></td>
<td><code class="docutils literal notranslate">b[j1:j2]</code> should be inserted at
<code class="docutils literal notranslate">a[i1:i1]</code>. Note that <code class="docutils literal notranslate">i1 == i2</code> in
this case.</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">'equal'</code></td>
<td><code class="docutils literal notranslate">a[i1:i2] == b[j1:j2]</code> (the sub-sequences
are equal).</td>
</tr>
</tbody>
</table>
For example:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; a = &quot;qabxcd&quot;
&gt;&gt;&gt; b = &quot;abycdf&quot;
&gt;&gt;&gt; s = SequenceMatcher(None, a, b)
&gt;&gt;&gt; for tag, i1, i2, j1, j2 in s.get_opcodes():
... print(&#39;{:7} a[{}:{}] --&gt; b[{}:{}] {!r:&gt;8} --&gt; {!r}&#39;.format(
... tag, i1, i2, j1, j2, a[i1:i2], b[j1:j2]))
delete a[0:1] --&gt; b[0:0] &#39;q&#39; --&gt; &#39;&#39;
equal a[1:3] --&gt; b[0:2] &#39;ab&#39; --&gt; &#39;ab&#39;
replace a[3:4] --&gt; b[2:3] &#39;x&#39; --&gt; &#39;y&#39;
equal a[4:6] --&gt; b[3:5] &#39;cd&#39; --&gt; &#39;cd&#39;
insert a[6:6] --&gt; b[5:6] &#39;&#39; --&gt; &#39;f&#39;
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="difflib.SequenceMatcher.get_grouped_opcodes">
<code class="descname">get_grouped_opcodes</code>(n=3)<a class="headerlink" href="#difflib.SequenceMatcher.get_grouped_opcodes" title="Permalink to this definition">¶</a></dt>
<dd>Return a <a class="reference internal" href="../glossary.html#term-generator">generator</a> of groups with up to n lines of context.
Starting with the groups returned by <a class="reference internal" href="#difflib.SequenceMatcher.get_opcodes" title="difflib.SequenceMatcher.get_opcodes"><code class="xref py py-meth docutils literal notranslate">get_opcodes()</code></a>, this method
splits out smaller change clusters and eliminates intervening ranges which
have no changes.
The groups are returned in the same format as <a class="reference internal" href="#difflib.SequenceMatcher.get_opcodes" title="difflib.SequenceMatcher.get_opcodes"><code class="xref py py-meth docutils literal notranslate">get_opcodes()</code></a>.
</dd></dl>

<dl class="method">
<dt id="difflib.SequenceMatcher.ratio">
<code class="descname">ratio</code>()<a class="headerlink" href="#difflib.SequenceMatcher.ratio" title="Permalink to this definition">¶</a></dt>
<dd>Return a measure of the sequences’ similarity as a float in the range [0,
1].
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 <code class="docutils literal notranslate">1.0</code> if the
sequences are identical, and <code class="docutils literal notranslate">0.0</code> if they have nothing in common.
This is expensive to compute if <a class="reference internal" href="#difflib.SequenceMatcher.get_matching_blocks" title="difflib.SequenceMatcher.get_matching_blocks"><code class="xref py py-meth docutils literal notranslate">get_matching_blocks()</code></a> or
<a class="reference internal" href="#difflib.SequenceMatcher.get_opcodes" title="difflib.SequenceMatcher.get_opcodes"><code class="xref py py-meth docutils literal notranslate">get_opcodes()</code></a> hasn’t already been called, in which case you may want
to try <a class="reference internal" href="#difflib.SequenceMatcher.quick_ratio" title="difflib.SequenceMatcher.quick_ratio"><code class="xref py py-meth docutils literal notranslate">quick_ratio()</code></a> or <a class="reference internal" href="#difflib.SequenceMatcher.real_quick_ratio" title="difflib.SequenceMatcher.real_quick_ratio"><code class="xref py py-meth docutils literal notranslate">real_quick_ratio()</code></a> first to get an
upper bound.
</dd></dl>

<dl class="method">
<dt id="difflib.SequenceMatcher.quick_ratio">
<code class="descname">quick_ratio</code>()<a class="headerlink" href="#difflib.SequenceMatcher.quick_ratio" title="Permalink to this definition">¶</a></dt>
<dd>Return an upper bound on <a class="reference internal" href="#difflib.SequenceMatcher.ratio" title="difflib.SequenceMatcher.ratio"><code class="xref py py-meth docutils literal notranslate">ratio()</code></a> relatively quickly.
</dd></dl>

<dl class="method">
<dt id="difflib.SequenceMatcher.real_quick_ratio">
<code class="descname">real_quick_ratio</code>()<a class="headerlink" href="#difflib.SequenceMatcher.real_quick_ratio" title="Permalink to this definition">¶</a></dt>
<dd>Return an upper bound on <a class="reference internal" href="#difflib.SequenceMatcher.ratio" title="difflib.SequenceMatcher.ratio"><code class="xref py py-meth docutils literal notranslate">ratio()</code></a> very quickly.
</dd></dl>

</dd></dl>

The three methods that return the ratio of matching to total characters can give
different results due to differing levels of approximation, although
<code class="xref py py-meth docutils literal notranslate">quick_ratio()</code> and <code class="xref py py-meth docutils literal notranslate">real_quick_ratio()</code> are always at least as large as
<code class="xref py py-meth docutils literal notranslate">ratio()</code>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; s = SequenceMatcher(None, &quot;abcd&quot;, &quot;bcde&quot;)
&gt;&gt;&gt; s.ratio()
0.75
&gt;&gt;&gt; s.quick_ratio()
0.75
&gt;&gt;&gt; s.real_quick_ratio()
1.0
</pre></div>
</div>
</div>
<div class="section" id="sequencematcher-examples">
<h2>6.3.2. SequenceMatcher Examples<a class="headerlink" href="#sequencematcher-examples" title="Permalink to this headline">¶</a></h2>
This example compares two strings, considering blanks to be “junk”:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; s = SequenceMatcher(lambda x: x == &quot; &quot;,
... &quot;private Thread currentThread;&quot;,
... &quot;private volatile Thread currentThread;&quot;)
</pre></div>
</div>
<code class="xref py py-meth docutils literal notranslate">ratio()</code> returns a float in [0, 1], measuring the similarity of the
sequences. As a rule of thumb, a <code class="xref py py-meth docutils literal notranslate">ratio()</code> value over 0.6 means the
sequences are close matches:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; print(round(s.ratio(), 3))
0.866
</pre></div>
</div>
If you’re only interested in where the sequences match,
<code class="xref py py-meth docutils literal notranslate">get_matching_blocks()</code> is handy:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; for block in s.get_matching_blocks():
... print(&quot;a[%d] and b[%d] match for %d elements&quot; % block)
a[0] and b[0] match for 8 elements
a[8] and b[17] match for 21 elements
a[29] and b[38] match for 0 elements
</pre></div>
</div>
Note that the last tuple returned by <code class="xref py py-meth docutils literal notranslate">get_matching_blocks()</code> is always a
dummy, <code class="docutils literal notranslate">(len(a), len(b), 0)</code>, and this is the only case in which the last
tuple element (number of elements matched) is <code class="docutils literal notranslate">0</code>.
If you want to know how to change the first sequence into the second, use
<code class="xref py py-meth docutils literal notranslate">get_opcodes()</code>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; for opcode in s.get_opcodes():
... print(&quot;%6s a[%d:%d] b[%d:%d]&quot; % opcode)
 equal a[0:8] b[0:8]
insert a[8:8] b[8:17]
 equal a[8:29] b[17:38]
</pre></div>
</div>
<div class="admonition seealso">
See also
<ul class="last simple">
<li>The <a class="reference internal" href="#difflib.get_close_matches" title="difflib.get_close_matches"><code class="xref py py-func docutils literal notranslate">get_close_matches()</code></a> function in this module which shows how
simple code building on <a class="reference internal" href="#difflib.SequenceMatcher" title="difflib.SequenceMatcher"><code class="xref py py-class docutils literal notranslate">SequenceMatcher</code></a> can be used to do useful
work.</li>
<li><a class="reference external" href="https://code.activestate.com/recipes/576729/">Simple version control recipe</a> for a small application
built with <a class="reference internal" href="#difflib.SequenceMatcher" title="difflib.SequenceMatcher"><code class="xref py py-class docutils literal notranslate">SequenceMatcher</code></a>.</li>
</ul>
</div>
</div>
<div class="section" id="differ-objects">
<h2>6.3.3. Differ Objects<a class="headerlink" href="#differ-objects" title="Permalink to this headline">¶</a></h2>
Note that <a class="reference internal" href="#difflib.Differ" title="difflib.Differ"><code class="xref py py-class docutils literal notranslate">Differ</code></a>-generated deltas make no claim to be minimal
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.
The <a class="reference internal" href="#difflib.Differ" title="difflib.Differ"><code class="xref py py-class docutils literal notranslate">Differ</code></a> class has this constructor:
<dl class="class">
<dt>
class <code class="descclassname">difflib.</code><code class="descname">Differ</code>(linejunk=None, charjunk=None)</dt>
<dd>Optional keyword parameters linejunk and charjunk are for filter functions
(or <code class="docutils literal notranslate">None</code>):
linejunk: A function that accepts a single string argument, and returns true
if the string is junk. The default is <code class="docutils literal notranslate">None</code>, meaning that no line is
considered junk.
charjunk: A function that accepts a single character argument (a string of
length 1), and returns true if the character is junk. The default is <code class="docutils literal notranslate">None</code>,
meaning that no character is considered junk.
These junk-filtering functions speed up matching to find
differences and do not cause any differing lines or characters to
be ignored. Read the description of the
<a class="reference internal" href="#difflib.SequenceMatcher.find_longest_match" title="difflib.SequenceMatcher.find_longest_match"><code class="xref py py-meth docutils literal notranslate">find_longest_match()</code></a> method’s isjunk
parameter for an explanation.
<a class="reference internal" href="#difflib.Differ" title="difflib.Differ"><code class="xref py py-class docutils literal notranslate">Differ</code></a> objects are used (deltas generated) via a single method:
<dl class="method">
<dt id="difflib.Differ.compare">
<code class="descname">compare</code>(a, b)<a class="headerlink" href="#difflib.Differ.compare" title="Permalink to this definition">¶</a></dt>
<dd>Compare two sequences of lines, and generate the delta (a sequence of lines).
Each sequence must contain individual single-line strings ending with
newlines. Such sequences can be obtained from the
<a class="reference internal" href="io.html#io.IOBase.readlines" title="io.IOBase.readlines"><code class="xref py py-meth docutils literal notranslate">readlines()</code></a> method of file-like objects. The delta
generated also consists of newline-terminated strings, ready to be
printed as-is via the <a class="reference internal" href="io.html#io.IOBase.writelines" title="io.IOBase.writelines"><code class="xref py py-meth docutils literal notranslate">writelines()</code></a> method of a
file-like object.
</dd></dl>

</dd></dl>

</div>
<div class="section" id="differ-example">
<h2>6.3.4. Differ Example<a class="headerlink" href="#differ-example" title="Permalink to this headline">¶</a></h2>
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 <code class="xref py py-meth docutils literal notranslate">readlines()</code> method of file-like objects):
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; text1 = &#39;&#39;&#39; 1. Beautiful is better than ugly.
... 2. Explicit is better than implicit.
... 3. Simple is better than complex.
... 4. Complex is better than complicated.
... &#39;&#39;&#39;.splitlines(keepends=True)
&gt;&gt;&gt; len(text1)
4
&gt;&gt;&gt; text1[0][-1]
&#39;\n&#39;
&gt;&gt;&gt; text2 = &#39;&#39;&#39; 1. Beautiful is better than ugly.
... 3. Simple is better than complex.
... 4. Complicated is better than complex.
... 5. Flat is better than nested.
... &#39;&#39;&#39;.splitlines(keepends=True)
</pre></div>
</div>
Next we instantiate a Differ object:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; d = Differ()
</pre></div>
</div>
Note that when instantiating a <a class="reference internal" href="#difflib.Differ" title="difflib.Differ"><code class="xref py py-class docutils literal notranslate">Differ</code></a> object we may pass functions to
filter out line and character “junk.” See the <a class="reference internal" href="#difflib.Differ" title="difflib.Differ"><code class="xref py py-meth docutils literal notranslate">Differ()</code></a> constructor for
details.
Finally, we compare the two:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; result = list(d.compare(text1, text2))
</pre></div>
</div>
<code class="docutils literal notranslate">result</code> is a list of strings, so let’s pretty-print it:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from pprint import pprint
&gt;&gt;&gt; pprint(result)
[&#39; 1. Beautiful is better than ugly.\n&#39;,
 &#39;- 2. Explicit is better than implicit.\n&#39;,
 &#39;- 3. Simple is better than complex.\n&#39;,
 &#39;+ 3. Simple is better than complex.\n&#39;,
 &#39;? ++\n&#39;,
 &#39;- 4. Complex is better than complicated.\n&#39;,
 &#39;? ^ ---- ^\n&#39;,
 &#39;+ 4. Complicated is better than complex.\n&#39;,
 &#39;? ++++ ^ ^\n&#39;,
 &#39;+ 5. Flat is better than nested.\n&#39;]
</pre></div>
</div>
As a single multi-line string it looks like this:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; import sys
&gt;&gt;&gt; sys.stdout.writelines(result)
 1. Beautiful is better than ugly.
- 2. Explicit is better than implicit.
- 3. Simple is better than complex.
+ 3. Simple is better than complex.
? ++
- 4. Complex is better than complicated.
? ^ ---- ^
+ 4. Complicated is better than complex.
? ++++ ^ ^
+ 5. Flat is better than nested.
</pre></div>
</div>
</div>
<div class="section" id="a-command-line-interface-to-difflib">
<h2>6.3.5. A command-line interface to difflib<a class="headerlink" href="#a-command-line-interface-to-difflib" title="Permalink to this headline">¶</a></h2>
This example shows how to use difflib to create a <code class="docutils literal notranslate">diff</code>-like utility.
It is also contained in the Python source distribution, as
<code class="file docutils literal notranslate">Tools/scripts/diff.py</code>.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>#!/usr/bin/env python3
&quot;&quot;&quot; Command line interface to difflib.py providing diffs in four formats:

* ndiff: lists every line and highlights interline changes.
* context: highlights clusters of changes in a before/after format.
* unified: highlights clusters of changes in an inline format.
* html: generates side by side comparison with change highlights.

&quot;&quot;&quot;

import sys, os, difflib, argparse
from datetime import datetime, timezone

def file_mtime(path):
 t = datetime.fromtimestamp(os.stat(path).st_mtime,
 timezone.utc)
 return t.astimezone().isoformat()

def main():

parser = argparse.ArgumentParser()
 parser.add_argument(&#39;-c&#39;, action=&#39;store_true&#39;, default=False,
 help=&#39;Produce a context format diff (default)&#39;)
 parser.add_argument(&#39;-u&#39;, action=&#39;store_true&#39;, default=False,
 help=&#39;Produce a unified format diff&#39;)
 parser.add_argument(&#39;-m&#39;, action=&#39;store_true&#39;, default=False,
 help=&#39;Produce HTML side by side diff &#39;
 &#39;(can use -c and -l in conjunction)&#39;)
 parser.add_argument(&#39;-n&#39;, action=&#39;store_true&#39;, default=False,
 help=&#39;Produce a ndiff format diff&#39;)
 parser.add_argument(&#39;-l&#39;, &#39;--lines&#39;, type=int, default=3,
 help=&#39;Set number of context lines (default 3)&#39;)
 parser.add_argument(&#39;fromfile&#39;)
 parser.add_argument(&#39;tofile&#39;)
 options = parser.parse_args()

n = options.lines
 fromfile = options.fromfile
 tofile = options.tofile

fromdate = file_mtime(fromfile)
 todate = file_mtime(tofile)
 with open(fromfile) as ff:
 fromlines = ff.readlines()
 with open(tofile) as tf:
 tolines = tf.readlines()

if options.u:
 diff = difflib.unified_diff(fromlines, tolines, fromfile, tofile, fromdate, todate, n=n)
 elif options.n:
 diff = difflib.ndiff(fromlines, tolines)
 elif options.m:
 diff = difflib.HtmlDiff().make_file(fromlines,tolines,fromfile,tofile,context=options.c,numlines=n)
 else:
 diff = difflib.context_diff(fromlines, tolines, fromfile, tofile, fromdate, todate, n=n)

sys.stdout.writelines(diff)

if __name__ == &#39;__main__&#39;:
 main()
</pre></div>
</div>
</div>
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 <ul>
<li><a class="reference internal" href="#">6.3. <code class="docutils literal notranslate">difflib</code> — Helpers for computing deltas</a><ul>
<li><a class="reference internal" href="#sequencematcher-objects">6.3.1. SequenceMatcher Objects</a></li>
<li><a class="reference internal" href="#sequencematcher-examples">6.3.2. SequenceMatcher Examples</a></li>
<li><a class="reference internal" href="#differ-objects">6.3.3. Differ Objects</a></li>
<li><a class="reference internal" href="#differ-example">6.3.4. Differ Example</a></li>
<li><a class="reference internal" href="#a-command-line-interface-to-difflib">6.3.5. A command-line interface to difflib</a></li>
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