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annotate Doc/lib/libxreadlines.tex @ 21467:4e35fa5d5708 legacy-trunk

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Add documentation for the help() built-in; contributed by Ka-Ping Yee. This is part of SF patch #494622.
author Fred Drake <fdrake@acm.org>
date Tue, 18 Dec 2001 16:31:08 +0000
parents 7ea30a163463
children 422784709380 ca907f28e2d5
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1 \section{\module{xreadlines} ---
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2 Efficient iteration over a file}
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3
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4 \declaremodule{extension}{xreadlines}
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5 \modulesynopsis{Efficient iteration over the lines of a file.}
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6
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7 \versionadded{2.1}
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8
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9
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10 This module defines a new object type which can efficiently iterate
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11 over the lines of a file. An xreadlines object is a sequence type
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12 which implements simple in-order indexing beginning at \code{0}, as
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13 required by \keyword{for} statement or the
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14 \function{filter()} function.
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15
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16 Thus, the code
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17
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18 \begin{verbatim}
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19 import xreadlines, sys
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20
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21 for line in xreadlines.xreadlines(sys.stdin):
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22 pass
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23 \end{verbatim}
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24
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25 has approximately the same speed and memory consumption as
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26
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27 \begin{verbatim}
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28 while 1:
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29 lines = sys.stdin.readlines(8*1024)
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30 if not lines: break
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31 for line in lines:
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32 pass
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33 \end{verbatim}
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34
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35 except the clarity of the \keyword{for} statement is retained in the
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36 former case.
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37
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38 \begin{funcdesc}{xreadlines}{fileobj}
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39 Return a new xreadlines object which will iterate over the contents
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40 of \var{fileobj}. \var{fileobj} must have a \method{readlines()}
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41 method that supports the \var{sizehint} parameter.
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42 \end{funcdesc}
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43
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44 An xreadlines object \var{s} supports the following sequence
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45 operation:
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46
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47 \begin{tableii}{c|l}{code}{Operation}{Result}
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48 \lineii{\var{s}[\var{i}]}{\var{i}'th line of \var{s}}
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49 \end{tableii}
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50
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51 If successive values of \var{i} are not sequential starting from
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52 \code{0}, this code will raise \exception{RuntimeError}.
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53
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54 After the last line of the file is read, this code will raise an
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55 \exception{IndexError}.