[Python-checkins] python/nondist/sandbox/string libstring.tex, NONE, 1.1

Wed Aug 11 00:27:48 CEST 2004

Update of /cvsroot/python/python/nondist/sandbox/string
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv15312
Added Files:
	libstring.tex 
Log Message:
Latest round of PEP 292 implementation after discussions w/Raymond. I think
we're basically ready for a thumbs up or down.
- Got rid of older versions alt292.py and pep292.py
- Got rid of safedict.py, which thanks to Raymond's we don't need to be able
 to retain braces in safe-substitutions
- Updated re-org of the string module -> package (not strictly a PEP 292
 proposal but something I still think is useful to do -- and backward
 compatibly transparent
- Updated documentation for the string package
- Updated tests
--- NEW FILE: libstring.tex ---
\section{\module{string} ---
 Common string operations}
\declaremodule{standard}{string}
\modulesynopsis{Common string operations.}
The \module{string} package contains a number of useful constants and classes,
as well as some deprecated legacy functions that are also available as methods
on strings. See the module \refmodule{re}\refstmodindex{re} for string
functions based on regular expressions.
In general, all of these objects are exposed directly in the \module{string}
package so users need only import the \module{string} package to begin using
these constants, classes, and functions.
\begin{notice}
Starting with Python 2.4, the traditional \module{string} module was turned
into a package, however backward compatibility with existing code has been
retained. Code using the \module{string} module that worked prior to Python
2.4 should continue to work unchanged.
\end{notice}
\subsection{String constants}
The constants defined in this module are:
\begin{datadesc}{ascii_letters}
 The concatenation of the \constant{ascii_lowercase} and
 \constant{ascii_uppercase} constants described below. This value is
 not locale-dependent.
\end{datadesc}
\begin{datadesc}{ascii_lowercase}
 The lowercase letters \code{'abcdefghijklmnopqrstuvwxyz'}. This
 value is not locale-dependent and will not change.
\end{datadesc}
\begin{datadesc}{ascii_uppercase}
 The uppercase letters \code{'ABCDEFGHIJKLMNOPQRSTUVWXYZ'}. This
 value is not locale-dependent and will not change.
\end{datadesc}
\begin{datadesc}{digits}
 The string \code{'0123456789'}.
\end{datadesc}
\begin{datadesc}{hexdigits}
 The string \code{'0123456789abcdefABCDEF'}.
\end{datadesc}
\begin{datadesc}{letters}
 The concatenation of the strings \constant{lowercase} and
 \constant{uppercase} described below. The specific value is
 locale-dependent, and will be updated when
 \function{locale.setlocale()} is called.
\end{datadesc}
\begin{datadesc}{lowercase}
 A string containing all the characters that are considered lowercase
 letters. On most systems this is the string
 \code{'abcdefghijklmnopqrstuvwxyz'}. Do not change its definition ---
 the effect on the routines \function{upper()} and
 \function{swapcase()} is undefined. The specific value is
 locale-dependent, and will be updated when
 \function{locale.setlocale()} is called.
\end{datadesc}
\begin{datadesc}{octdigits}
 The string \code{'01234567'}.
\end{datadesc}
\begin{datadesc}{punctuation}
 String of \ASCII{} characters which are considered punctuation
 characters in the \samp{C} locale.
\end{datadesc}
\begin{datadesc}{printable}
 String of characters which are considered printable. This is a
 combination of \constant{digits}, \constant{letters},
 \constant{punctuation}, and \constant{whitespace}.
\end{datadesc}
\begin{datadesc}{uppercase}
 A string containing all the characters that are considered uppercase
 letters. On most systems this is the string
 \code{'ABCDEFGHIJKLMNOPQRSTUVWXYZ'}. Do not change its definition ---
 the effect on the routines \function{lower()} and
 \function{swapcase()} is undefined. The specific value is
 locale-dependent, and will be updated when
 \function{locale.setlocale()} is called.
\end{datadesc}
\begin{datadesc}{whitespace}
 A string containing all characters that are considered whitespace.
 On most systems this includes the characters space, tab, linefeed,
 return, formfeed, and vertical tab. Do not change its definition ---
 the effect on the routines \function{strip()} and \function{split()}
 is undefined.
\end{datadesc}
\subsection{Template strings}
Templates are Unicode strings that can be used to provide simpler string
substitutions as described in \pep{292}. There is a \class{template} class
that is a subclass of \class{unicode}, overriding the default
\method{__mod__()} method. Instead of the normal
\samp{\%}-based substitutions, template strings support \samp{\$}-based
substitutions, using the following rules:
\begin{itemize}
\item \samp{\$\$} is an escape; it is replaced with a single \samp{\$}.
\item \samp{\$identifier} names a substitution placeholder matching a mapping
 key of "identifier". By default, "identifier" must spell a Python
 identifier. The first non-identifier character after the \samp{\$}
 character terminates this placeholder specification.
\item \samp{\$\{identifier\}} is equivalent to \samp{\$identifier}. It is
 required when valid identifier characters follow the placeholder but are
 not part of the placeholder, e.g. "\$\{noun\}ification".
\end{itemize}
Template strings are used just like normal strings, in that the modulus
operator is used to interpolate a dictionary of values into a template string,
e.g.:
\begin{verbatim}
>>> from string import template
>>> s = template('$who likes $what')
>>> print s % dict(who='tim', what='kung pao')
tim likes kung pao
\end{verbatim}
There is also a \class{safe_template} class, derived from \class{template}
which acts the same as \class{template}, except that if placeholders are
missing in the interpolation dictionary, no \exception{KeyError} will be
raised. Instead the original placeholder (with or without the braces, as
appropriate) will be used:
\begin{verbatim}
>>> from string import safe_template
>>> s = safe_template('$who likes $what for ${meal}')
>>> print s % dict(who='tim')
tim likes $what for ${meal}
\end{verbatim}
Advanced usage: you can derive subclasses of \class{template} or
\class{safe_template} to use application-specific placeholder rules. To do
this, you override the class attribute \member{pattern}; the value must be a
compiled regular expression object with three capturing groups. The capturing
groups correspond to the three rules given above.
\subsection{String functions}
The following functions are available to operate on string and Unicode
objects. They are not available as string methods.
\begin{funcdesc}{capwords}{s}
 Split the argument into words using \function{split()}, capitalize
 each word using \function{capitalize()}, and join the capitalized
 words using \function{join()}. Note that this replaces runs of
 whitespace characters by a single space, and removes leading and
 trailing whitespace.
\end{funcdesc}
\begin{funcdesc}{maketrans}{from, to}
 Return a translation table suitable for passing to
 \function{translate()} or \function{regex.compile()}, that will map
 each character in \var{from} into the character at the same position
 in \var{to}; \var{from} and \var{to} must have the same length.
 \warning{Don't use strings derived from \constant{lowercase}
 and \constant{uppercase} as arguments; in some locales, these don't have
 the same length. For case conversions, always use
 \function{lower()} and \function{upper()}.}
\end{funcdesc}
\subsection{Deprecated string functions}
The following list of functions are also defined as methods of string and
Unicode objects; see ``String Methods'' (section
\ref{string-methods}) for more information on those. You should consider
these functions as deprecated, although they will not be removed until Python
3.0. The functions defined in this module are:
\begin{funcdesc}{atof}{s}
 \deprecated{2.0}{Use the \function{float()} built-in function.}
 Convert a string to a floating point number. The string must have
 the standard syntax for a floating point literal in Python,
 optionally preceded by a sign (\samp{+} or \samp{-}). Note that
 this behaves identical to the built-in function
 \function{float()}\bifuncindex{float} when passed a string.
 \note{When passing in a string, values for NaN\index{NaN}
 and Infinity\index{Infinity} may be returned, depending on the
 underlying C library. The specific set of strings accepted which
 cause these values to be returned depends entirely on the C library
 and is known to vary.}
\end{funcdesc}
\begin{funcdesc}{atoi}{s\optional{, base}}
 \deprecated{2.0}{Use the \function{int()} built-in function.}
 Convert string \var{s} to an integer in the given \var{base}. The
 string must consist of one or more digits, optionally preceded by a
 sign (\samp{+} or \samp{-}). The \var{base} defaults to 10. If it
 is 0, a default base is chosen depending on the leading characters
 of the string (after stripping the sign): \samp{0x} or \samp{0X}
 means 16, \samp{0} means 8, anything else means 10. If \var{base}
 is 16, a leading \samp{0x} or \samp{0X} is always accepted, though
 not required. This behaves identically to the built-in function
 \function{int()} when passed a string. (Also note: for a more
 flexible interpretation of numeric literals, use the built-in
 function \function{eval()}\bifuncindex{eval}.)
\end{funcdesc}
\begin{funcdesc}{atol}{s\optional{, base}}
 \deprecated{2.0}{Use the \function{long()} built-in function.}
 Convert string \var{s} to a long integer in the given \var{base}.
 The string must consist of one or more digits, optionally preceded
 by a sign (\samp{+} or \samp{-}). The \var{base} argument has the
 same meaning as for \function{atoi()}. A trailing \samp{l} or
 \samp{L} is not allowed, except if the base is 0. Note that when
 invoked without \var{base} or with \var{base} set to 10, this
 behaves identical to the built-in function
 \function{long()}\bifuncindex{long} when passed a string.
\end{funcdesc}
\begin{funcdesc}{capitalize}{word}
 Return a copy of \var{word} with only its first character capitalized.
\end{funcdesc}
\begin{funcdesc}{expandtabs}{s\optional{, tabsize}}
 Expand tabs in a string, i.e.\ replace them by one or more spaces,
 depending on the current column and the given tab size. The column
 number is reset to zero after each newline occurring in the string.
 This doesn't understand other non-printing characters or escape
 sequences. The tab size defaults to 8.
\end{funcdesc}
\begin{funcdesc}{find}{s, sub\optional{, start\optional{,end}}}
 Return the lowest index in \var{s} where the substring \var{sub} is
 found such that \var{sub} is wholly contained in
 \code{\var{s}[\var{start}:\var{end}]}. Return \code{-1} on failure.
 Defaults for \var{start} and \var{end} and interpretation of
 negative values is the same as for slices.
\end{funcdesc}
\begin{funcdesc}{rfind}{s, sub\optional{, start\optional{, end}}}
 Like \function{find()} but find the highest index.
\end{funcdesc}
\begin{funcdesc}{index}{s, sub\optional{, start\optional{, end}}}
 Like \function{find()} but raise \exception{ValueError} when the
 substring is not found.
\end{funcdesc}
\begin{funcdesc}{rindex}{s, sub\optional{, start\optional{, end}}}
 Like \function{rfind()} but raise \exception{ValueError} when the
 substring is not found.
\end{funcdesc}
\begin{funcdesc}{count}{s, sub\optional{, start\optional{, end}}}
 Return the number of (non-overlapping) occurrences of substring
 \var{sub} in string \code{\var{s}[\var{start}:\var{end}]}.
 Defaults for \var{start} and \var{end} and interpretation of
 negative values are the same as for slices.
\end{funcdesc}
\begin{funcdesc}{lower}{s}
 Return a copy of \var{s}, but with upper case letters converted to
 lower case.
\end{funcdesc}
\begin{funcdesc}{split}{s\optional{, sep\optional{, maxsplit}}}
 Return a list of the words of the string \var{s}. If the optional
 second argument \var{sep} is absent or \code{None}, the words are
 separated by arbitrary strings of whitespace characters (space, tab, 
 newline, return, formfeed). If the second argument \var{sep} is
 present and not \code{None}, it specifies a string to be used as the 
 word separator. The returned list will then have one more item
 than the number of non-overlapping occurrences of the separator in
 the string. The optional third argument \var{maxsplit} defaults to
 0. If it is nonzero, at most \var{maxsplit} number of splits occur,
 and the remainder of the string is returned as the final element of
 the list (thus, the list will have at most \code{\var{maxsplit}+1}
 elements).
 The behavior of split on an empty string depends on the value of \var{sep}.
 If \var{sep} is not specified, or specified as \code{None}, the result will
 be an empty list. If \var{sep} is specified as any string, the result will
 be a list containing one element which is an empty string.
\end{funcdesc}
\begin{funcdesc}{rsplit}{s\optional{, sep\optional{, maxsplit}}}
 Return a list of the words of the string \var{s}, scanning \var{s}
 from the end. To all intents and purposes, the resulting list of
 words is the same as returned by \function{split()}, except when the
 optional third argument \var{maxsplit} is explicitly specified and
 nonzero. When \var{maxsplit} is nonzero, at most \var{maxsplit}
 number of splits -- the \emph{rightmost} ones -- occur, and the remainder
 of the string is returned as the first element of the list (thus, the
 list will have at most \code{\var{maxsplit}+1} elements).
 \versionadded{2.4}
\end{funcdesc}
\begin{funcdesc}{splitfields}{s\optional{, sep\optional{, maxsplit}}}
 This function behaves identically to \function{split()}. (In the
 past, \function{split()} was only used with one argument, while
 \function{splitfields()} was only used with two arguments.)
\end{funcdesc}
\begin{funcdesc}{join}{words\optional{, sep}}
 Concatenate a list or tuple of words with intervening occurrences of 
 \var{sep}. The default value for \var{sep} is a single space
 character. It is always true that
 \samp{string.join(string.split(\var{s}, \var{sep}), \var{sep})}
 equals \var{s}.
\end{funcdesc}
\begin{funcdesc}{joinfields}{words\optional{, sep}}
 This function behaves identically to \function{join()}. (In the past, 
 \function{join()} was only used with one argument, while
 \function{joinfields()} was only used with two arguments.)
 Note that there is no \method{joinfields()} method on string
 objects; use the \method{join()} method instead.
\end{funcdesc}
\begin{funcdesc}{lstrip}{s\optional{, chars}}
Return a copy of the string with leading characters removed. If
\var{chars} is omitted or \code{None}, whitespace characters are
removed. If given and not \code{None}, \var{chars} must be a string;
the characters in the string will be stripped from the beginning of
the string this method is called on.
\versionchanged[The \var{chars} parameter was added. The \var{chars}
parameter cannot be passed in earlier 2.2 versions]{2.2.3}
\end{funcdesc}
\begin{funcdesc}{rstrip}{s\optional{, chars}}
Return a copy of the string with trailing characters removed. If
\var{chars} is omitted or \code{None}, whitespace characters are
removed. If given and not \code{None}, \var{chars} must be a string;
the characters in the string will be stripped from the end of the
string this method is called on.
\versionchanged[The \var{chars} parameter was added. The \var{chars}
parameter cannot be passed in earlier 2.2 versions]{2.2.3}
\end{funcdesc}
\begin{funcdesc}{strip}{s\optional{, chars}}
Return a copy of the string with leading and trailing characters
removed. If \var{chars} is omitted or \code{None}, whitespace
characters are removed. If given and not \code{None}, \var{chars}
must be a string; the characters in the string will be stripped from
the both ends of the string this method is called on.
\versionchanged[The \var{chars} parameter was added. The \var{chars}
parameter cannot be passed in earlier 2.2 versions]{2.2.3}
\end{funcdesc}
\begin{funcdesc}{swapcase}{s}
 Return a copy of \var{s}, but with lower case letters
 converted to upper case and vice versa.
\end{funcdesc}
\begin{funcdesc}{translate}{s, table\optional{, deletechars}}
 Delete all characters from \var{s} that are in \var{deletechars} (if 
 present), and then translate the characters using \var{table}, which 
 must be a 256-character string giving the translation for each
 character value, indexed by its ordinal.
\end{funcdesc}
\begin{funcdesc}{upper}{s}
 Return a copy of \var{s}, but with lower case letters converted to
 upper case.
\end{funcdesc}
\begin{funcdesc}{ljust}{s, width}
\funcline{rjust}{s, width}
\funcline{center}{s, width}
 These functions respectively left-justify, right-justify and center
 a string in a field of given width. They return a string that is at
 least \var{width} characters wide, created by padding the string
 \var{s} with spaces until the given width on the right, left or both
 sides. The string is never truncated.
\end{funcdesc}
\begin{funcdesc}{zfill}{s, width}
 Pad a numeric string on the left with zero digits until the given
 width is reached. Strings starting with a sign are handled
 correctly.
\end{funcdesc}
\begin{funcdesc}{replace}{str, old, new\optional{, maxreplace}}
 Return a copy of string \var{str} with all occurrences of substring
 \var{old} replaced by \var{new}. If the optional argument
 \var{maxreplace} is given, the first \var{maxreplace} occurrences are
 replaced.
\end{funcdesc}