source: trunk/essentials/dev-lang/python/Doc/lib/libtextwrap.tex@ 3368

\section{\module{textwrap} ---
         Text wrapping and filling}

\declaremodule{standard}{textwrap}
\modulesynopsis{Text wrapping and filling}
\moduleauthor{Greg Ward}{[email protected]}
\sectionauthor{Greg Ward}{[email protected]}

\versionadded{2.3}

The \module{textwrap} module provides two convenience functions,
\function{wrap()} and \function{fill()}, as well as
\class{TextWrapper}, the class that does all the work, and a utility function 
\function{dedent()}.  If you're just wrapping or filling one or two 
text strings, the convenience functions should be good enough; otherwise, 
you should use an instance of \class{TextWrapper} for efficiency.

\begin{funcdesc}{wrap}{text\optional{, width\optional{, \moreargs}}}
Wraps the single paragraph in \var{text} (a string) so every line is at
most \var{width} characters long.  Returns a list of output lines,
without final newlines.

Optional keyword arguments correspond to the instance attributes of
\class{TextWrapper}, documented below.  \var{width} defaults to
\code{70}.
\end{funcdesc}

\begin{funcdesc}{fill}{text\optional{, width\optional{, \moreargs}}}
Wraps the single paragraph in \var{text}, and returns a single string
containing the wrapped paragraph.  \function{fill()} is shorthand for
\begin{verbatim}
"\n".join(wrap(text, ...))
\end{verbatim}

In particular, \function{fill()} accepts exactly the same keyword
arguments as \function{wrap()}.
\end{funcdesc}

Both \function{wrap()} and \function{fill()} work by creating a
\class{TextWrapper} instance and calling a single method on it.  That
instance is not reused, so for applications that wrap/fill many text
strings, it will be more efficient for you to create your own
\class{TextWrapper} object.

An additional utility function, \function{dedent()}, is provided to
remove indentation from strings that have unwanted whitespace to the
left of the text.

\begin{funcdesc}{dedent}{text} 
Remove any common leading whitespace from every line in \var{text}.

This can be used to make triple-quoted strings line up with the left
edge of the display, while still presenting them in the source code
in indented form.

Note that tabs and spaces are both treated as whitespace, but they are
not equal: the lines \code{" {} hello"} and \code{"\textbackslash{}thello"}
are considered to have no common leading whitespace.  (This behaviour is
new in Python 2.5; older versions of this module incorrectly expanded
tabs before searching for common leading whitespace.)

For example:
\begin{verbatim}
def test():
    # end first line with \ to avoid the empty line!
    s = '''\
    hello
      world
    '''
    print repr(s)          # prints '    hello\n      world\n    '
    print repr(dedent(s))  # prints 'hello\n  world\n'
\end{verbatim}
\end{funcdesc}

\begin{classdesc}{TextWrapper}{...}
The \class{TextWrapper} constructor accepts a number of optional
keyword arguments.  Each argument corresponds to one instance attribute,
so for example
\begin{verbatim}
wrapper = TextWrapper(initial_indent="* ")
\end{verbatim}
is the same as
\begin{verbatim}
wrapper = TextWrapper()
wrapper.initial_indent = "* "
\end{verbatim}

You can re-use the same \class{TextWrapper} object many times, and you
can change any of its options through direct assignment to instance
attributes between uses.
\end{classdesc}

The \class{TextWrapper} instance attributes (and keyword arguments to
the constructor) are as follows:

\begin{memberdesc}{width}
(default: \code{70}) The maximum length of wrapped lines.  As long as
there are no individual words in the input text longer than
\member{width}, \class{TextWrapper} guarantees that no output line
will be longer than \member{width} characters.
\end{memberdesc}

\begin{memberdesc}{expand_tabs}
(default: \code{True}) If true, then all tab characters in \var{text}
will be expanded to spaces using the \method{expandtabs()} method of
\var{text}.
\end{memberdesc}

\begin{memberdesc}{replace_whitespace}
(default: \code{True}) If true, each whitespace character (as defined
by \code{string.whitespace}) remaining after tab expansion will be
replaced by a single space.  \note{If \member{expand_tabs} is false
and \member{replace_whitespace} is true, each tab character will be
replaced by a single space, which is \emph{not} the same as tab
expansion.}
\end{memberdesc}

\begin{memberdesc}{initial_indent}
(default: \code{''}) String that will be prepended to the first line
of wrapped output.  Counts towards the length of the first line.
\end{memberdesc}

\begin{memberdesc}{subsequent_indent}
(default: \code{''}) String that will be prepended to all lines of
wrapped output except the first.  Counts towards the length of each
line except the first.
\end{memberdesc}

\begin{memberdesc}{fix_sentence_endings}
(default: \code{False}) If true, \class{TextWrapper} attempts to detect
sentence endings and ensure that sentences are always separated by
exactly two spaces.  This is generally desired for text in a monospaced
font.  However, the sentence detection algorithm is imperfect: it
assumes that a sentence ending consists of a lowercase letter followed
by one of \character{.},
\character{!}, or \character{?}, possibly followed by one of
\character{"} or \character{'}, followed by a space.  One problem
with this is algorithm is that it is unable to detect the difference
between ``Dr.'' in

\begin{verbatim}
[...] Dr. Frankenstein's monster [...]
\end{verbatim}

and ``Spot.'' in

\begin{verbatim}
[...] See Spot. See Spot run [...]
\end{verbatim}

\member{fix_sentence_endings} is false by default.

Since the sentence detection algorithm relies on
\code{string.lowercase} for the definition of ``lowercase letter,''
and a convention of using two spaces after a period to separate
sentences on the same line, it is specific to English-language texts.
\end{memberdesc}

\begin{memberdesc}{break_long_words}
(default: \code{True}) If true, then words longer than
\member{width} will be broken in order to ensure that no lines are
longer than \member{width}.  If it is false, long words will not be
broken, and some lines may be longer than \member{width}.  (Long words
will be put on a line by themselves, in order to minimize the amount
by which \member{width} is exceeded.)
\end{memberdesc}

\class{TextWrapper} also provides two public methods, analogous to the
module-level convenience functions:

\begin{methoddesc}{wrap}{text}
Wraps the single paragraph in \var{text} (a string) so every line is
at most \member{width} characters long.  All wrapping options are
taken from instance attributes of the \class{TextWrapper} instance.
Returns a list of output lines, without final newlines.
\end{methoddesc}

\begin{methoddesc}{fill}{text}
Wraps the single paragraph in \var{text}, and returns a single string
containing the wrapped paragraph.
\end{methoddesc}