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| 55 | <H2><A NAME="SECTION006420000000000000000"></A><A NAME="sequencematcher-examples"></A> | |
| 56 | <BR> | |
| 57 | 4.4.2 SequenceMatcher Examples | |
| 58 | </H2> | |
| 59 | ||
| 60 | <P> | |
| 61 | This example compares two strings, considering blanks to be ``junk:'' | |
| 62 | ||
| 63 | <P> | |
| 64 | <div class="verbatim"><pre> | |
| 65 | >>> s = SequenceMatcher(lambda x: x == " ", | |
| 66 | ... "private Thread currentThread;", | |
| 67 | ... "private volatile Thread currentThread;") | |
| 68 | </pre></div> | |
| 69 | ||
| 70 | <P> | |
| 71 | <tt class="method">ratio()</tt> returns a float in [0, 1], measuring the similarity | |
| 72 | of the sequences. As a rule of thumb, a <tt class="method">ratio()</tt> value over | |
| 73 | 0.6 means the sequences are close matches: | |
| 74 | ||
| 75 | <P> | |
| 76 | <div class="verbatim"><pre> | |
| 77 | >>> print round(s.ratio(), 3) | |
| 78 | 0.866 | |
| 79 | </pre></div> | |
| 80 | ||
| 81 | <P> | |
| 82 | If you're only interested in where the sequences match, | |
| 83 | <tt class="method">get_matching_blocks()</tt> is handy: | |
| 84 | ||
| 85 | <P> | |
| 86 | <div class="verbatim"><pre> | |
| 87 | >>> for block in s.get_matching_blocks(): | |
| 88 | ... print "a[%d] and b[%d] match for %d elements" % block | |
| 89 | a[0] and b[0] match for 8 elements | |
| 90 | a[8] and b[17] match for 6 elements | |
| 91 | a[14] and b[23] match for 15 elements | |
| 92 | a[29] and b[38] match for 0 elements | |
| 93 | </pre></div> | |
| 94 | ||
| 95 | <P> | |
| 96 | Note that the last tuple returned by <tt class="method">get_matching_blocks()</tt> is | |
| 97 | always a dummy, <code>(len(<var>a</var>), len(<var>b</var>), 0)</code>, and this is | |
| 98 | the only case in which the last tuple element (number of elements | |
| 99 | matched) is <code>0</code>. | |
| 100 | ||
| 101 | <P> | |
| 102 | If you want to know how to change the first sequence into the second, | |
| 103 | use <tt class="method">get_opcodes()</tt>: | |
| 104 | ||
| 105 | <P> | |
| 106 | <div class="verbatim"><pre> | |
| 107 | >>> for opcode in s.get_opcodes(): | |
| 108 | ... print "%6s a[%d:%d] b[%d:%d]" % opcode | |
| 109 | equal a[0:8] b[0:8] | |
| 110 | insert a[8:8] b[8:17] | |
| 111 | equal a[8:14] b[17:23] | |
| 112 | equal a[14:29] b[23:38] | |
| 113 | </pre></div> | |
| 114 | ||
| 115 | <P> | |
| 116 | See also the function <tt class="function">get_close_matches()</tt> in this module, | |
| 117 | which shows how simple code building on <tt class="class">SequenceMatcher</tt> can be | |
| 118 | used to do useful work. | |
| 119 | ||
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