.. 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>
Source code: :source:`Lib/fileinput.py`
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`.
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 and the optional arguments mode and openhook
are ignored. 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:`OSError` is raised.
.. versionchanged:: 3.3 :exc:`IOError` used to be raised; it is now an alias of :exc:`OSError`.
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=None, inplace=False, backup='', *, mode='r', openhook=None)
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.
The :class:`FileInput` instance can be used as a context manager in the
:keyword:`with` statement. In this example, *input* is closed after the
:keyword:`!with` statement is exited, even if an exception occurs::
with fileinput.input(files=('spam.txt', 'eggs.txt')) as f:
for line in f:
process(line)
.. versionchanged:: 3.2
Can be used as a context manager.
.. versionchanged:: 3.8
The keyword parameters *mode* and *openhook* are now keyword-only.
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``.
.. 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() Return ``True`` if the line just read is the first line of its file, otherwise return ``False``.
.. function:: isstdin() Return ``True`` if the last line was read from ``sys.stdin``, otherwise return ``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:
Optional in-place filtering: if the keyword argument inplace=True 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.
The two following opening hooks are provided by this module:
.. 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)``
.. function:: hook_encoded(encoding, errors=None)
Returns a hook which opens each file with :func:`open`, using the given
*encoding* and *errors* to read the file.
Usage example: ``fi =
fileinput.FileInput(openhook=fileinput.hook_encoded("utf-8",
"surrogateescape"))``
.. versionchanged:: 3.6
Added the optional *errors* parameter.
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