248 lines
9.5 KiB
TeX
248 lines
9.5 KiB
TeX
\section{Standard Module \sectcode{string}}
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\label{module-string}
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\stmodindex{string}
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This module defines some constants useful for checking character
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classes and some useful string functions. See the modules
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\code{regex} and \code{regsub} for string functions based on regular
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expressions.
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The constants defined in this module are are:
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\renewcommand{\indexsubitem}{(data in module string)}
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\begin{datadesc}{digits}
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The string \code{'0123456789'}.
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\end{datadesc}
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\begin{datadesc}{hexdigits}
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The string \code{'0123456789abcdefABCDEF'}.
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\end{datadesc}
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\begin{datadesc}{letters}
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The concatenation of the strings \code{lowercase} and
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\code{uppercase} described below.
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\end{datadesc}
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\begin{datadesc}{lowercase}
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A string containing all the characters that are considered lowercase
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letters. On most systems this is the string
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\code{'abcdefghijklmnopqrstuvwxyz'}. Do not change its definition ---
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the effect on the routines \code{upper} and \code{swapcase} is
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undefined.
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\end{datadesc}
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\begin{datadesc}{octdigits}
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The string \code{'01234567'}.
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\end{datadesc}
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\begin{datadesc}{uppercase}
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A string containing all the characters that are considered uppercase
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letters. On most systems this is the string
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\code{'ABCDEFGHIJKLMNOPQRSTUVWXYZ'}. Do not change its definition ---
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the effect on the routines \code{lower} and \code{swapcase} is
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undefined.
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\end{datadesc}
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\begin{datadesc}{whitespace}
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A string containing all characters that are considered whitespace.
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On most systems this includes the characters space, tab, linefeed,
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return, formfeed, and vertical tab. Do not change its definition ---
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the effect on the routines \code{strip} and \code{split} is
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undefined.
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\end{datadesc}
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The functions defined in this module are:
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\renewcommand{\indexsubitem}{(in module string)}
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\begin{funcdesc}{atof}{s}
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Convert a string to a floating point number. The string must have
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the standard syntax for a floating point literal in Python, optionally
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preceded by a sign (\samp{+} or \samp{-}). Note that this behaves
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identical to the built-in function \code{float()} when passed a string.
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\end{funcdesc}
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\begin{funcdesc}{atoi}{s\optional{\, base}}
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Convert string \var{s} to an integer in the given \var{base}. The
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string must consist of one or more digits, optionally preceded by a
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sign (\samp{+} or \samp{-}). The \var{base} defaults to 10. If it is
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0, a default base is chosen depending on the leading characters of the
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string (after stripping the sign): \samp{0x} or \samp{0X} means 16,
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\samp{0} means 8, anything else means 10. If \var{base} is 16, a
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leading \samp{0x} or \samp{0X} is always accepted. Note that when
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invoked without \var{base} or with \var{base} set to 10, this behaves
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identical to the built-in function \code{int()} when passed a string.
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(Also note: for a more flexible interpretation of numeric literals,
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use the built-in function \code{eval()}.)
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\bifuncindex{eval}
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\end{funcdesc}
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\begin{funcdesc}{atol}{s\optional{\, base}}
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Convert string \var{s} to a long integer in the given \var{base}. The
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string must consist of one or more digits, optionally preceded by a
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sign (\samp{+} or \samp{-}). The \var{base} argument has the same
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meaning as for \code{atoi()}. A trailing \samp{l} or \samp{L} is not
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allowed, except if the base is 0. Note that when invoked without
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\var{base} or with \var{base} set to 10, this behaves identical to the
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built-in function \code{long()} when passed a string.
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\end{funcdesc}
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\begin{funcdesc}{capitalize}{word}
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Capitalize the first character of the argument.
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\end{funcdesc}
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\begin{funcdesc}{capwords}{s}
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Split the argument into words using \code{split}, capitalize each word
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using \code{capitalize}, and join the capitalized words using
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\code{join}. Note that this replaces runs of whitespace characters by
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a single space. (See also \code{regsub.capwords()} for a version
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that doesn't change the delimiters, and lets you specify a word
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separator.)
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\end{funcdesc}
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\begin{funcdesc}{expandtabs}{s\, tabsize}
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Expand tabs in a string, i.e.\ replace them by one or more spaces,
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depending on the current column and the given tab size. The column
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number is reset to zero after each newline occurring in the string.
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This doesn't understand other non-printing characters or escape
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sequences.
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\end{funcdesc}
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\begin{funcdesc}{find}{s\, sub\optional{\, start\optional{\,end}}}
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Return the lowest index in \var{s} where the substring \var{sub} is
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found such that \var{sub} is wholly contained in
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\code{\var{s}[\var{start}:\var{end}]}. Return -1 on failure.
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Defaults for \var{start} and \var{end} and interpretation of negative
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values is the same as for slices.
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\end{funcdesc}
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\begin{funcdesc}{rfind}{s\, sub\optional{\, start\optional{\,end}}}
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Like \code{find} but find the highest index.
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\end{funcdesc}
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\begin{funcdesc}{index}{s\, sub\optional{\, start\optional{\,end}}}
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Like \code{find} but raise \code{ValueError} when the substring is
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not found.
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\end{funcdesc}
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\begin{funcdesc}{rindex}{s\, sub\optional{\, start\optional{\,end}}}
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Like \code{rfind} but raise \code{ValueError} when the substring is
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not found.
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\end{funcdesc}
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\begin{funcdesc}{count}{s\, sub\optional{\, start\optional{\,end}}}
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Return the number of (non-overlapping) occurrences of substring
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\var{sub} in string \code{\var{s}[\var{start}:\var{end}]}.
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Defaults for \var{start} and \var{end} and interpretation of negative
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values is the same as for slices.
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\end{funcdesc}
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\begin{funcdesc}{lower}{s}
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Convert letters to lower case.
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\end{funcdesc}
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\begin{funcdesc}{maketrans}{from, to}
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Return a translation table suitable for passing to \code{string.translate}
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or \code{regex.compile}, that will map each character in \var{from}
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into the character at the same position in \var{to}; \var{from} and
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\var{to} must have the same length.
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\end{funcdesc}
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\begin{funcdesc}{split}{s\optional{\, sep\optional{\, maxsplit}}}
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Return a list of the words of the string \var{s}. If the optional
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second argument \var{sep} is absent or \code{None}, the words are
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separated by arbitrary strings of whitespace characters (space, tab,
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newline, return, formfeed). If the second argument \var{sep} is
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present and not \code{None}, it specifies a string to be used as the
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word separator. The returned list will then have one more items than
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the number of non-overlapping occurrences of the separator in the
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string. The optional third argument \var{maxsplit} defaults to 0. If
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it is nonzero, at most \var{maxsplit} number of splits occur, and the
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remainder of the string is returned as the final element of the list
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(thus, the list will have at most \code{\var{maxsplit}+1} elements).
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(See also \code{regsub.split()} for a version that allows specifying a
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regular expression as the separator.)
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\end{funcdesc}
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\begin{funcdesc}{splitfields}{s\optional{\, sep\optional{\, maxsplit}}}
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This function behaves identically to \code{split}. (In the past,
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\code{split} was only used with one argument, while \code{splitfields}
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was only used with two arguments.)
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\end{funcdesc}
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\begin{funcdesc}{join}{words\optional{\, sep}}
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Concatenate a list or tuple of words with intervening occurrences of
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\var{sep}. The default value for \var{sep} is a single space character.
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It is always true that
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\code{string.join(string.split(\var{s}, \var{sep}), \var{sep})}
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equals \var{s}.
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\end{funcdesc}
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\begin{funcdesc}{joinfields}{words\optional{\, sep}}
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This function behaves identical to \code{join}. (In the past,
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\code{join} was only used with one argument, while \code{joinfields}
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was only used with two arguments.)
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\end{funcdesc}
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\begin{funcdesc}{lstrip}{s}
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Remove leading whitespace from the string \var{s}.
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\end{funcdesc}
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\begin{funcdesc}{rstrip}{s}
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Remove trailing whitespace from the string \var{s}.
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\end{funcdesc}
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\begin{funcdesc}{strip}{s}
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Remove leading and trailing whitespace from the string \var{s}.
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\end{funcdesc}
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\begin{funcdesc}{swapcase}{s}
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Convert lower case letters to upper case and vice versa.
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\end{funcdesc}
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\begin{funcdesc}{translate}{s, table\optional{, deletechars}}
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Delete all characters from \var{s} that are in \var{deletechars} (if present), and
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then translate the characters using \var{table}, which must be
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a 256-character string giving the translation for each character
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value, indexed by its ordinal.
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\end{funcdesc}
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\begin{funcdesc}{upper}{s}
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Convert letters to upper case.
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\end{funcdesc}
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\begin{funcdesc}{ljust}{s\, width}
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\funcline{rjust}{s\, width}
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\funcline{center}{s\, width}
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These functions respectively left-justify, right-justify and center a
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string in a field of given width.
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They return a string that is at least
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\var{width}
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characters wide, created by padding the string
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\var{s}
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with spaces until the given width on the right, left or both sides.
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The string is never truncated.
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\end{funcdesc}
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\begin{funcdesc}{zfill}{s\, width}
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Pad a numeric string on the left with zero digits until the given
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width is reached. Strings starting with a sign are handled correctly.
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\end{funcdesc}
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\begin{funcdesc}{replace}{str, old, new\optional{, maxsplit}}
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Return a copy of string \var{str} with all occurrences of substring
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\var{old} replaced by \var{new}. If the optional argument
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\var{maxsplit} is given, the first \var{maxsplit} occurrences are
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replaced.
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\end{funcdesc}
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This module is implemented in Python. Much of its functionality has
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been reimplemented in the built-in module \code{strop}. However, you
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should \emph{never} import the latter module directly. When
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\code{string} discovers that \code{strop} exists, it transparently
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replaces parts of itself with the implementation from \code{strop}.
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After initialization, there is \emph{no} overhead in using
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\code{string} instead of \code{strop}.
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\bimodindex{strop}
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