cpython/Doc/library/textwrap.rst

:mod:`textwrap` --- Text wrapping and filling
=============================================

.. module:: textwrap
   :synopsis: Text wrapping and filling
.. moduleauthor:: Greg Ward <gward@python.net>
.. sectionauthor:: Greg Ward <gward@python.net>


The :mod:`textwrap` module provides two convenience functions, :func:`wrap` and
:func:`fill`, as well as :class:`TextWrapper`, the class that does all the work,
and a utility function  :func:`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.


.. function:: wrap(text[, width[, ...]])

   Wraps the single paragraph in *text* (a string) so every line is at most *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.  *width* defaults to ``70``.


.. function:: fill(text[, width[, ...]])

   Wraps the single paragraph in *text*, and returns a single string containing the
   wrapped paragraph.  :func:`fill` is shorthand for  ::

      "\n".join(wrap(text, ...))

   In particular, :func:`fill` accepts exactly the same keyword arguments as
   :func:`wrap`.

Both :func:`wrap` and :func:`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, :func:`dedent`, is provided to remove
indentation from strings that have unwanted whitespace to the left of the text.


.. function:: dedent(text)

   Remove any common leading whitespace from every line in *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 ``"  hello"`` and ``"\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::

      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'


.. class:: TextWrapper(...)

   The :class:`TextWrapper` constructor accepts a number of optional keyword
   arguments.  Each argument corresponds to one instance attribute, so for example
   ::

      wrapper = TextWrapper(initial_indent="* ")

   is the same as  ::

      wrapper = TextWrapper()
      wrapper.initial_indent = "* "

   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.

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


.. attribute:: TextWrapper.width

   (default: ``70``) The maximum length of wrapped lines.  As long as there are no
   individual words in the input text longer than :attr:`width`,
   :class:`TextWrapper` guarantees that no output line will be longer than
   :attr:`width` characters.


.. attribute:: TextWrapper.expand_tabs

   (default: ``True``) If true, then all tab characters in *text* will be expanded
   to spaces using the :meth:`expandtabs` method of *text*.


.. attribute:: TextWrapper.replace_whitespace

   (default: ``True``) If true, each whitespace character (as defined by
   ``string.whitespace``) remaining after tab expansion will be replaced by a
   single space.

   .. note::

      If :attr:`expand_tabs` is false and :attr:`replace_whitespace` is true, each tab
      character will be replaced by a single space, which is *not* the same as tab
      expansion.


.. attribute:: TextWrapper.drop_whitespace

   (default: ``True``) If true, whitespace that, after wrapping, happens to end up
   at the beginning or end of a line is dropped (leading whitespace in the first
   line is always preserved, though).


.. attribute:: TextWrapper.initial_indent

   (default: ``''``) String that will be prepended to the first line of wrapped
   output.  Counts towards the length of the first line.


.. attribute:: TextWrapper.subsequent_indent

   (default: ``''``) String that will be prepended to all lines of wrapped output
   except the first.  Counts towards the length of each line except the first.


.. attribute:: TextWrapper.fix_sentence_endings

   (default: ``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 ``'.'``, ``'!'``, or ``'?'``, possibly
   followed by one of ``'"'`` or ``"'"``, followed by a space.  One problem with
   this is algorithm is that it is unable to detect the difference between "Dr." in
   ::

      [...] Dr. Frankenstein's monster [...]

   and "Spot." in ::

      [...] See Spot. See Spot run [...]

   :attr:`fix_sentence_endings` is false by default.

   Since the sentence detection algorithm relies on ``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.


.. attribute:: TextWrapper.break_long_words

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

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


.. method:: TextWrapper.wrap(text)

   Wraps the single paragraph in *text* (a string) so every line is at most
   :attr:`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.


.. method:: TextWrapper.fill(text)

   Wraps the single paragraph in *text*, and returns a single string containing the
   wrapped paragraph.