4.4.2 SequenceMatcher Examples
Keywords: lib

##
4.4.2 SequenceMatcher Examples

This example compares two strings, considering blanks to be ``junk:''

      >>> s = SequenceMatcher(lambda x: x == " ",
      ...                     "private Thread currentThread;",
      ...                     "private volatile Thread currentThread;")

`ratio()` returns a float in [0, 1], measuring the similarity of the sequences. As a rule of thumb, a `ratio()` value over 0.6 means the sequences are close matches:

      >>> print round(s.ratio(), 3)
      0.866

If you're only interested in where the sequences match, `get_matching_blocks()` is handy:

      >>> 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

Note that the last tuple returned by `get_matching_blocks()` is always a dummy, `(len(a), len(b), 0)`, and this is the only case in which the last tuple element (number of elements matched) is `0`.

If you want to know how to change the first sequence into the second, use `get_opcodes()`:

      >>> 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]

See also the function `get_close_matches()` in this module, which shows how simple code building on `SequenceMatcher` can be used to do useful work.