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#2986 Add autojunk parameter to SequenceMatcher to optionally disable 'popular == junk' heuristic.

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Terry Reedy 2010-11-11 23:22:19 +00:00
parent 6c2e0224ff
commit d2d2ae91c5
4 changed files with 96 additions and 39 deletions
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Doc/library/difflib.rst
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@ -37,6 +37,16 @@ diffs. For comparing directories and files, see also, the :mod:`filecmp` module.
complicated way on how many elements the sequences have in common; best case
time is linear.
**Automatic junk heuristic:** :class:`SequenceMatcher` 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 ``autojunk`` argument to ``False`` when creating the :class:`SequenceMatcher`.
.. versionadded:: 2.7
The *autojunk* parameter.
.. class:: Differ
@ -334,7 +344,7 @@ SequenceMatcher Objects
The :class:`SequenceMatcher` class has this constructor:
.. class:: SequenceMatcher([isjunk[, a[, b]]])
.. class:: SequenceMatcher([isjunk[, a[, b[, autojunk=True]]]])
Optional argument *isjunk* must be ``None`` (the default) or a one-argument
function that takes a sequence element and returns true if and only if the
@ -350,6 +360,9 @@ The :class:`SequenceMatcher` class has this constructor:
The optional arguments *a* and *b* are sequences to be compared; both default to
empty strings. The elements of both sequences must be :term:`hashable`.
The optional argument *autojunk* can be used to disable the automatic junk
heuristic.
:class:`SequenceMatcher` objects have the following methods: