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<H2><A NAME="SECTION006420000000000000000"></A><A NAME="sequencematcher-examples"></A>
<BR>
4.4.2 SequenceMatcher Examples
</H2>
<P>
This example compares two strings, considering blanks to be ``junk:''
<P>
<div class="verbatim"><pre>
>>> s = SequenceMatcher(lambda x: x == " ",
... "private Thread currentThread;",
... "private volatile Thread currentThread;")
</pre></div>
<P>
<tt class="method">ratio()</tt> returns a float in [0, 1], measuring the similarity
of the sequences. As a rule of thumb, a <tt class="method">ratio()</tt> value over
0.6 means the sequences are close matches:
<P>
<div class="verbatim"><pre>
>>> print round(s.ratio(), 3)
0.866
</pre></div>
<P>
If you're only interested in where the sequences match,
<tt class="method">get_matching_blocks()</tt> is handy:
<P>
<div class="verbatim"><pre>
>>> for block in s.get_matching_blocks():
... print "a[%d] and b[%d] match for %d elements" % block
a[0] and b[0] match for 8 elements
a[8] and b[17] match for 6 elements
a[14] and b[23] match for 15 elements
a[29] and b[38] match for 0 elements
</pre></div>
<P>
Note that the last tuple returned by <tt class="method">get_matching_blocks()</tt> is
always a dummy, <code>(len(<var>a</var>), len(<var>b</var>), 0)</code>, and this is
the only case in which the last tuple element (number of elements
matched) is <code>0</code>.
<P>
If you want to know how to change the first sequence into the second,
use <tt class="method">get_opcodes()</tt>:
<P>
<div class="verbatim"><pre>
>>> for opcode in s.get_opcodes():
... print "%6s a[%d:%d] b[%d:%d]" % opcode
equal a[0:8] b[0:8]
insert a[8:8] b[8:17]
equal a[8:14] b[17:23]
equal a[14:29] b[23:38]
</pre></div>
<P>
See also the function <tt class="function">get_close_matches()</tt> in this module,
which shows how simple code building on <tt class="class">SequenceMatcher</tt> can be
used to do useful work.
<P>
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<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
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