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276 lines
11 KiB
TeX
276 lines
11 KiB
TeX
\section{\module{string} ---
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Common string operations}
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\declaremodule{standard}{string}
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\modulesynopsis{Common string operations.}
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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 module
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\refmodule{re}\refstmodindex{re} for string functions based on regular
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expressions.
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The constants defined in this module are:
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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 \constant{lowercase} and
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\constant{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 \function{upper()} and
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\function{swapcase()} is 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}{punctuation}
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String of \ASCII{} characters which are considered punctuation
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characters in the \samp{C} locale.
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\end{datadesc}
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\begin{datadesc}{printable}
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String of characters which are considered printable. This is a
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combination of \constant{digits}, \constant{letters},
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\constant{punctuation}, and \constant{whitespace}.
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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 \function{lower()} and
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\function{swapcase()} is 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 \function{strip()} and \function{split()}
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is undefined.
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\end{datadesc}
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Many of the functions provided by this module are also defined as
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methods of string and Unicode objects; see ``String Methods'' (section
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\ref{string-methods}) for more information on those.
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The functions defined in this module are:
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\begin{funcdesc}{atof}{s}
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\deprecated{2.0}{Use the \function{float()} built-in function.}
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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,
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optionally preceded by a sign (\samp{+} or \samp{-}). Note that
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this behaves identical to the built-in function
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\function{float()}\bifuncindex{float} when passed a string.
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\strong{Note:} When passing in a string, values for NaN\index{NaN}
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and Infinity\index{Infinity} may be returned, depending on the
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underlying C library. The specific set of strings accepted which
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cause these values to be returned depends entirely on the C library
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and is known to vary.
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\end{funcdesc}
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\begin{funcdesc}{atoi}{s\optional{, base}}
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\deprecated{2.0}{Use the \function{int()} built-in function.}
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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
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is 0, a default base is chosen depending on the leading characters
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of the string (after stripping the sign): \samp{0x} or \samp{0X}
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means 16, \samp{0} means 8, anything else means 10. If \var{base}
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is 16, a leading \samp{0x} or \samp{0X} is always accepted, though
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not required. This behaves identically to the built-in function
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\function{int()} when passed a string. (Also note: for a more
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flexible interpretation of numeric literals, use the built-in
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function \function{eval()}\bifuncindex{eval}.)
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\end{funcdesc}
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\begin{funcdesc}{atol}{s\optional{, base}}
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\deprecated{2.0}{Use the \function{long()} built-in function.}
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Convert string \var{s} to a long integer in the given \var{base}.
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The string must consist of one or more digits, optionally preceded
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by a sign (\samp{+} or \samp{-}). The \var{base} argument has the
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same meaning as for \function{atoi()}. A trailing \samp{l} or
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\samp{L} is not allowed, except if the base is 0. Note that when
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invoked without \var{base} or with \var{base} set to 10, this
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behaves identical to the built-in function
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\function{long()}\bifuncindex{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 \function{split()}, capitalize
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each word using \function{capitalize()}, and join the capitalized
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words using \function{join()}. Note that this replaces runs of
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whitespace characters by a single space, and removes leading and
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trailing whitespace.
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\end{funcdesc}
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\begin{funcdesc}{expandtabs}{s\optional{, 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. The tab size defaults to 8.
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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 \code{-1} on failure.
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Defaults for \var{start} and \var{end} and interpretation of
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negative 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 \function{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 \function{find()} but raise \exception{ValueError} when the
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substring is 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 \function{rfind()} but raise \exception{ValueError} when the
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substring is 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
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negative values are the same as for slices.
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\end{funcdesc}
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\begin{funcdesc}{lower}{s}
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Return a copy of \var{s}, but with upper case letters converted to
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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
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\function{translate()} or \function{regex.compile()}, that will map
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each character in \var{from} into the character at the same position
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in \var{to}; \var{from} and \var{to} must have the same length.
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\strong{Warning:} don't use strings derived from \constant{lowercase}
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and \constant{uppercase} as arguments; in some locales, these don't have
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the same length. For case conversions, always use
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\function{lower()} and \function{upper()}.
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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 item
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than the number of non-overlapping occurrences of the separator in
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the string. The optional third argument \var{maxsplit} defaults to
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0. If it is nonzero, at most \var{maxsplit} number of splits occur,
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and the remainder of the string is returned as the final element of
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the list (thus, the list will have at most \code{\var{maxsplit}+1}
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elements).
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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 \function{split()}. (In the
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past, \function{split()} was only used with one argument, while
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\function{splitfields()} 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
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character. It is always true that
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\samp{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 \function{join()}. (In the past,
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\function{join()} was only used with one argument, while
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\function{joinfields()} was only used with two arguments.)
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\end{funcdesc}
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\begin{funcdesc}{lstrip}{s}
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Return a copy of \var{s} but without leading whitespace characters.
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\end{funcdesc}
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\begin{funcdesc}{rstrip}{s}
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Return a copy of \var{s} but without trailing whitespace
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characters.
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\end{funcdesc}
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\begin{funcdesc}{strip}{s}
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Return a copy of \var{s} without leading or trailing whitespace.
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\end{funcdesc}
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\begin{funcdesc}{swapcase}{s}
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Return a copy of \var{s}, but with lower case letters
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converted 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
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present), and then translate the characters using \var{table}, which
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must be a 256-character string giving the translation for each
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character value, indexed by its ordinal.
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\end{funcdesc}
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\begin{funcdesc}{upper}{s}
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Return a copy of \var{s}, but with lower case letters converted to
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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
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a string in a field of given width. They return a string that is at
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least \var{width} characters wide, created by padding the string
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\var{s} with spaces until the given width on the right, left or both
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sides. 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
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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
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\module{strop}\refbimodindex{strop}. However, you
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should \emph{never} import the latter module directly. When
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\module{string} discovers that \module{strop} exists, it transparently
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replaces parts of itself with the implementation from \module{strop}.
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After initialization, there is \emph{no} overhead in using
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\module{string} instead of \module{strop}.
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