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56 lines
2 KiB
TeX
56 lines
2 KiB
TeX
% 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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\section{\module{bisect} ---
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Array bisection algorithm}
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\declaremodule{standard}{bisect}
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\modulesynopsis{Array bisection algorithms for binary searching.}
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This module provides support for maintaining a list in sorted order
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without having to sort the list after each insertion. For long lists
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of items with expensive comparison operations, this can be an
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improvement over the more common approach. The module is called
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\module{bisect} because it uses a basic bisection algorithm to do its
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work. The source code may be most useful as a working example of the
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algorithm (i.e., the boundary conditions are already right!).
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The following functions are provided:
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\begin{funcdesc}{bisect}{list, item\optional{, lo\optional{, hi}}}
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Locate the proper insertion point for \var{item} in \var{list} to
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maintain sorted order. The parameters \var{lo} and \var{hi} may be
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used to specify a subset of the list which should be considered. The
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return value is suitable for use as the first parameter to
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\code{\var{list}.insert()}.
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\end{funcdesc}
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\begin{funcdesc}{insort}{list, item\optional{, lo\optional{, hi}}}
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Insert \var{item} in \var{list} in sorted order. This is equivalent
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to \code{\var{list}.insert(bisect.bisect(\var{list}, \var{item},
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\var{lo}, \var{hi}), \var{item})}.
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\end{funcdesc}
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\subsection{Example}
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\nodename{bisect-example}
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The \function{bisect()} function is generally useful for categorizing
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numeric data. This example uses \function{bisect()} to look up a
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letter grade for an exam total (say) based on a set of ordered numeric
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breakpoints: 85 and up is an `A', 75..84 is a `B', etc.
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\begin{verbatim}
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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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\end{verbatim}
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