85 lines
2.7 KiB
ReStructuredText
85 lines
2.7 KiB
ReStructuredText
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:mod:`bisect` --- Array bisection algorithm
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===========================================
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.. module:: bisect
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:synopsis: Array bisection algorithms for binary searching.
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.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
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.. % LaTeX produced by Fred L. Drake, Jr. <fdrake@acm.org>, with an
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.. % example based on the PyModules FAQ entry by Aaron Watters
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.. % <arw@pythonpros.com>.
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This module provides support for maintaining a list in sorted order without
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having to sort the list after each insertion. For long lists of items with
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expensive comparison operations, this can be an improvement over the more common
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approach. The module is called :mod:`bisect` because it uses a basic bisection
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algorithm to do its work. The source code may be most useful as a working
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example of the algorithm (the boundary conditions are already right!).
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The following functions are provided:
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.. function:: bisect_left(list, item[, lo[, hi]])
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Locate the proper insertion point for *item* in *list* to maintain sorted order.
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The parameters *lo* and *hi* may be used to specify a subset of the list which
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should be considered; by default the entire list is used. If *item* is already
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present in *list*, the insertion point will be before (to the left of) any
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existing entries. The return value is suitable for use as the first parameter
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to ``list.insert()``. This assumes that *list* is already sorted.
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.. function:: bisect_right(list, item[, lo[, hi]])
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Similar to :func:`bisect_left`, but returns an insertion point which comes after
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(to the right of) any existing entries of *item* in *list*.
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.. function:: bisect(...)
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Alias for :func:`bisect_right`.
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.. function:: insort_left(list, item[, lo[, hi]])
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Insert *item* in *list* in sorted order. This is equivalent to
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``list.insert(bisect.bisect_left(list, item, lo, hi), item)``. This assumes
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that *list* is already sorted.
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.. function:: insort_right(list, item[, lo[, hi]])
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Similar to :func:`insort_left`, but inserting *item* in *list* after any
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existing entries of *item*.
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.. function:: insort(...)
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Alias for :func:`insort_right`.
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Examples
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--------
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.. _bisect-example:
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The :func:`bisect` function is generally useful for categorizing numeric data.
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This example uses :func:`bisect` to look up a letter grade for an exam total
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(say) based on a set of ordered numeric breakpoints: 85 and up is an 'A', 75..84
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is a 'B', etc. ::
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>>> grades = "FEDCBA"
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>>> breakpoints = [30, 44, 66, 75, 85]
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>>> from bisect import bisect
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>>> def grade(total):
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... return grades[bisect(breakpoints, total)]
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...
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>>> grade(66)
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'C'
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>>> map(grade, [33, 99, 77, 44, 12, 88])
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['E', 'A', 'B', 'D', 'F', 'A']
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