cpython/Doc/library/fileinput.rst

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:mod:`fileinput` --- Iterate over lines from multiple input streams
===================================================================
.. module:: fileinput
:synopsis: Loop over standard input or a list of files.
.. moduleauthor:: Guido van Rossum <guido@python.org>
.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
This module implements a helper class and functions to quickly write a
loop over standard input or a list of files. If you just want to read or
write one file see :func:`open`.
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The typical use is::
import fileinput
for line in fileinput.input():
process(line)
This iterates over the lines of all files listed in ``sys.argv[1:]``, defaulting
to ``sys.stdin`` if the list is empty. If a filename is ``'-'``, it is also
replaced by ``sys.stdin``. To specify an alternative list of filenames, pass it
as the first argument to :func:`input`. A single file name is also allowed.
All files are opened in text mode by default, but you can override this by
specifying the *mode* parameter in the call to :func:`input` or
:class:`FileInput()`. If an I/O error occurs during opening or reading a file,
:exc:`IOError` is raised.
If ``sys.stdin`` is used more than once, the second and further use will return
no lines, except perhaps for interactive use, or if it has been explicitly reset
(e.g. using ``sys.stdin.seek(0)``).
Empty files are opened and immediately closed; the only time their presence in
the list of filenames is noticeable at all is when the last file opened is
empty.
Lines are returned with any newlines intact, which means that the last line in
a file may not have one.
You can control how files are opened by providing an opening hook via the
*openhook* parameter to :func:`fileinput.input` or :class:`FileInput()`. The
hook must be a function that takes two arguments, *filename* and *mode*, and
returns an accordingly opened file-like object. Two useful hooks are already
provided by this module.
The following function is the primary interface of this module:
.. function:: input([files[, inplace[, backup[, mode[, openhook]]]]])
Create an instance of the :class:`FileInput` class. The instance will be used
as global state for the functions of this module, and is also returned to use
during iteration. The parameters to this function will be passed along to the
constructor of the :class:`FileInput` class.
.. versionchanged:: 2.5
Added the *mode* and *openhook* parameters.
The following functions use the global state created by :func:`fileinput.input`;
if there is no active state, :exc:`RuntimeError` is raised.
.. function:: filename()
Return the name of the file currently being read. Before the first line has
been read, returns ``None``.
.. function:: fileno()
Return the integer "file descriptor" for the current file. When no file is
opened (before the first line and between files), returns ``-1``.
.. versionadded:: 2.5
.. function:: lineno()
Return the cumulative line number of the line that has just been read. Before
the first line has been read, returns ``0``. After the last line of the last
file has been read, returns the line number of that line.
.. function:: filelineno()
Return the line number in the current file. Before the first line has been
read, returns ``0``. After the last line of the last file has been read,
returns the line number of that line within the file.
.. function:: isfirstline()
Returns true if the line just read is the first line of its file, otherwise
returns false.
.. function:: isstdin()
Returns true if the last line was read from ``sys.stdin``, otherwise returns
false.
.. function:: nextfile()
Close the current file so that the next iteration will read the first line from
the next file (if any); lines not read from the file will not count towards the
cumulative line count. The filename is not changed until after the first line
of the next file has been read. Before the first line has been read, this
function has no effect; it cannot be used to skip the first file. After the
last line of the last file has been read, this function has no effect.
.. function:: close()
Close the sequence.
The class which implements the sequence behavior provided by the module is
available for subclassing as well:
.. class:: FileInput([files[, inplace[, backup[, mode[, openhook]]]]])
Class :class:`FileInput` is the implementation; its methods :meth:`filename`,
:meth:`fileno`, :meth:`lineno`, :meth:`filelineno`, :meth:`isfirstline`,
:meth:`isstdin`, :meth:`nextfile` and :meth:`close` correspond to the functions
of the same name in the module. In addition it has a :meth:`readline` method
which returns the next input line, and a :meth:`__getitem__` method which
implements the sequence behavior. The sequence must be accessed in strictly
sequential order; random access and :meth:`readline` cannot be mixed.
With *mode* you can specify which file mode will be passed to :func:`open`. It
must be one of ``'r'``, ``'rU'``, ``'U'`` and ``'rb'``.
The *openhook*, when given, must be a function that takes two arguments,
*filename* and *mode*, and returns an accordingly opened file-like object. You
cannot use *inplace* and *openhook* together.
.. versionchanged:: 2.5
Added the *mode* and *openhook* parameters.
**Optional in-place filtering:** if the keyword argument ``inplace=1`` is passed
to :func:`fileinput.input` or to the :class:`FileInput` constructor, the file is
moved to a backup file and standard output is directed to the input file (if a
file of the same name as the backup file already exists, it will be replaced
silently). This makes it possible to write a filter that rewrites its input
file in place. If the *backup* parameter is given (typically as
``backup='.<some extension>'``), it specifies the extension for the backup file,
and the backup file remains around; by default, the extension is ``'.bak'`` and
it is deleted when the output file is closed. In-place filtering is disabled
when standard input is read.
.. warning::
Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r68133 | antoine.pitrou | 2009-01-01 16:38:03 +0100 (Thu, 01 Jan 2009) | 1 line fill in actual issue number in tests ........ r68134 | hirokazu.yamamoto | 2009-01-01 16:45:39 +0100 (Thu, 01 Jan 2009) | 2 lines Issue #4797: IOError.filename was not set when _fileio.FileIO failed to open file with `str' filename on Windows. ........ r68141 | benjamin.peterson | 2009-01-01 17:43:12 +0100 (Thu, 01 Jan 2009) | 1 line fix highlighting ........ r68142 | benjamin.peterson | 2009-01-01 18:29:49 +0100 (Thu, 01 Jan 2009) | 2 lines welcome to 2009, Python! ........ r68145 | amaury.forgeotdarc | 2009-01-02 01:03:54 +0100 (Fri, 02 Jan 2009) | 5 lines #4801 _collections module fails to build on cygwin. _PyObject_GC_TRACK is the macro version of PyObject_GC_Track, and according to documentation it should not be used for extension modules. ........ r68146 | ronald.oussoren | 2009-01-02 11:44:46 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue4472: "configure --enable-shared doesn't work on OSX" ........ r68148 | ronald.oussoren | 2009-01-02 11:48:31 +0100 (Fri, 02 Jan 2009) | 2 lines Forgot to add a NEWS item in my previous checkin ........ r68149 | ronald.oussoren | 2009-01-02 11:50:48 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue4780 ........ r68159 | ronald.oussoren | 2009-01-02 15:48:17 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue 1627952 ........ r68160 | ronald.oussoren | 2009-01-02 15:52:09 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue r1737832 ........ r68161 | ronald.oussoren | 2009-01-02 16:00:05 +0100 (Fri, 02 Jan 2009) | 3 lines Fix for issue 1149804 ........ r68162 | ronald.oussoren | 2009-01-02 16:06:00 +0100 (Fri, 02 Jan 2009) | 3 lines Fix for issue 4472 is incompatible with Cygwin, this patch should fix that. ........ r68166 | benjamin.peterson | 2009-01-02 19:26:23 +0100 (Fri, 02 Jan 2009) | 1 line document PyMemberDef ........ r68171 | georg.brandl | 2009-01-02 21:25:14 +0100 (Fri, 02 Jan 2009) | 3 lines #4811: fix markup glitches (mostly remains of the conversion), found by Gabriel Genellina. ........ r68172 | martin.v.loewis | 2009-01-02 21:32:55 +0100 (Fri, 02 Jan 2009) | 2 lines Issue #4075: Use OutputDebugStringW in Py_FatalError. ........ r68173 | martin.v.loewis | 2009-01-02 21:40:14 +0100 (Fri, 02 Jan 2009) | 2 lines Issue #4051: Prevent conflict of UNICODE macros in cPickle. ........ r68174 | benjamin.peterson | 2009-01-02 21:47:27 +0100 (Fri, 02 Jan 2009) | 1 line fix compilation on non-Windows platforms ........ r68179 | raymond.hettinger | 2009-01-02 22:26:45 +0100 (Fri, 02 Jan 2009) | 1 line Issue #4615. Document how to use itertools for de-duping. ........ r68195 | georg.brandl | 2009-01-03 14:45:15 +0100 (Sat, 03 Jan 2009) | 2 lines Remove useless string literal. ........ r68196 | georg.brandl | 2009-01-03 15:29:53 +0100 (Sat, 03 Jan 2009) | 2 lines Fix indentation. ........ r68210 | georg.brandl | 2009-01-03 20:10:12 +0100 (Sat, 03 Jan 2009) | 2 lines Set eol-style correctly for mp_distributing.py. ........ r68214 | georg.brandl | 2009-01-03 20:44:48 +0100 (Sat, 03 Jan 2009) | 2 lines Make indentation consistent. ........ r68215 | georg.brandl | 2009-01-03 21:15:14 +0100 (Sat, 03 Jan 2009) | 2 lines Fix role name. ........ r68217 | georg.brandl | 2009-01-03 21:30:15 +0100 (Sat, 03 Jan 2009) | 2 lines Add rstlint, a little tool to find subtle markup problems and inconsistencies in the Doc sources. ........ r68218 | georg.brandl | 2009-01-03 21:38:59 +0100 (Sat, 03 Jan 2009) | 2 lines Recognize usage of the default role. ........ r68219 | georg.brandl | 2009-01-03 21:47:01 +0100 (Sat, 03 Jan 2009) | 2 lines Fix uses of the default role. ........ r68220 | georg.brandl | 2009-01-03 21:55:06 +0100 (Sat, 03 Jan 2009) | 2 lines Remove trailing whitespace. ........ r68221 | georg.brandl | 2009-01-03 22:04:55 +0100 (Sat, 03 Jan 2009) | 2 lines Remove tabs from the documentation. ........ r68222 | georg.brandl | 2009-01-03 22:11:58 +0100 (Sat, 03 Jan 2009) | 2 lines Disable the line length checker by default. ........
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The current implementation does not work for MS-DOS 8+3 filesystems.
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The two following opening hooks are provided by this module:
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.. function:: hook_compressed(filename, mode)
Transparently opens files compressed with gzip and bzip2 (recognized by the
extensions ``'.gz'`` and ``'.bz2'``) using the :mod:`gzip` and :mod:`bz2`
modules. If the filename extension is not ``'.gz'`` or ``'.bz2'``, the file is
opened normally (ie, using :func:`open` without any decompression).
Usage example: ``fi = fileinput.FileInput(openhook=fileinput.hook_compressed)``
.. versionadded:: 2.5
.. function:: hook_encoded(encoding)
Returns a hook which opens each file with :func:`codecs.open`, using the given
*encoding* to read the file.
Usage example: ``fi =
fileinput.FileInput(openhook=fileinput.hook_encoded("iso-8859-1"))``
.. note::
With this hook, :class:`FileInput` might return Unicode strings depending on the
specified *encoding*.
.. versionadded:: 2.5