1 :mod:`fileinput` --- Iterate over lines from multiple input streams
2 ===================================================================
5 :synopsis: Loop over standard input or a list of files.
6 .. moduleauthor:: Guido van Rossum <guido@python.org>
7 .. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
10 This module implements a helper class and functions to quickly write a
11 loop over standard input or a list of files. If you just want to read or
12 write one file see :func:`open`.
17 for line in fileinput.input():
20 This iterates over the lines of all files listed in ``sys.argv[1:]``, defaulting
21 to ``sys.stdin`` if the list is empty. If a filename is ``'-'``, it is also
22 replaced by ``sys.stdin``. To specify an alternative list of filenames, pass it
23 as the first argument to :func:`.input`. A single file name is also allowed.
25 All files are opened in text mode by default, but you can override this by
26 specifying the *mode* parameter in the call to :func:`.input` or
27 :class:`FileInput()`. If an I/O error occurs during opening or reading a file,
28 :exc:`IOError` is raised.
30 If ``sys.stdin`` is used more than once, the second and further use will return
31 no lines, except perhaps for interactive use, or if it has been explicitly reset
32 (e.g. using ``sys.stdin.seek(0)``).
34 Empty files are opened and immediately closed; the only time their presence in
35 the list of filenames is noticeable at all is when the last file opened is
38 Lines are returned with any newlines intact, which means that the last line in
39 a file may not have one.
41 You can control how files are opened by providing an opening hook via the
42 *openhook* parameter to :func:`fileinput.input` or :class:`FileInput()`. The
43 hook must be a function that takes two arguments, *filename* and *mode*, and
44 returns an accordingly opened file-like object. Two useful hooks are already
45 provided by this module.
47 The following function is the primary interface of this module:
50 .. function:: input([files[, inplace[, backup[, mode[, openhook]]]]])
52 Create an instance of the :class:`FileInput` class. The instance will be used
53 as global state for the functions of this module, and is also returned to use
54 during iteration. The parameters to this function will be passed along to the
55 constructor of the :class:`FileInput` class.
57 .. versionchanged:: 2.5
58 Added the *mode* and *openhook* parameters.
60 The following functions use the global state created by :func:`fileinput.input`;
61 if there is no active state, :exc:`RuntimeError` is raised.
64 .. function:: filename()
66 Return the name of the file currently being read. Before the first line has
67 been read, returns ``None``.
70 .. function:: fileno()
72 Return the integer "file descriptor" for the current file. When no file is
73 opened (before the first line and between files), returns ``-1``.
78 .. function:: lineno()
80 Return the cumulative line number of the line that has just been read. Before
81 the first line has been read, returns ``0``. After the last line of the last
82 file has been read, returns the line number of that line.
85 .. function:: filelineno()
87 Return the line number in the current file. Before the first line has been
88 read, returns ``0``. After the last line of the last file has been read,
89 returns the line number of that line within the file.
92 .. function:: isfirstline()
94 Returns true if the line just read is the first line of its file, otherwise
98 .. function:: isstdin()
100 Returns true if the last line was read from ``sys.stdin``, otherwise returns
104 .. function:: nextfile()
106 Close the current file so that the next iteration will read the first line from
107 the next file (if any); lines not read from the file will not count towards the
108 cumulative line count. The filename is not changed until after the first line
109 of the next file has been read. Before the first line has been read, this
110 function has no effect; it cannot be used to skip the first file. After the
111 last line of the last file has been read, this function has no effect.
114 .. function:: close()
118 The class which implements the sequence behavior provided by the module is
119 available for subclassing as well:
122 .. class:: FileInput([files[, inplace[, backup[, mode[, openhook]]]]])
124 Class :class:`FileInput` is the implementation; its methods :meth:`filename`,
125 :meth:`fileno`, :meth:`lineno`, :meth:`filelineno`, :meth:`isfirstline`,
126 :meth:`isstdin`, :meth:`nextfile` and :meth:`close` correspond to the functions
127 of the same name in the module. In addition it has a :meth:`readline` method
128 which returns the next input line, and a :meth:`__getitem__` method which
129 implements the sequence behavior. The sequence must be accessed in strictly
130 sequential order; random access and :meth:`readline` cannot be mixed.
132 With *mode* you can specify which file mode will be passed to :func:`open`. It
133 must be one of ``'r'``, ``'rU'``, ``'U'`` and ``'rb'``.
135 The *openhook*, when given, must be a function that takes two arguments,
136 *filename* and *mode*, and returns an accordingly opened file-like object. You
137 cannot use *inplace* and *openhook* together.
139 .. versionchanged:: 2.5
140 Added the *mode* and *openhook* parameters.
142 **Optional in-place filtering:** if the keyword argument ``inplace=1`` is passed
143 to :func:`fileinput.input` or to the :class:`FileInput` constructor, the file is
144 moved to a backup file and standard output is directed to the input file (if a
145 file of the same name as the backup file already exists, it will be replaced
146 silently). This makes it possible to write a filter that rewrites its input
147 file in place. If the *backup* parameter is given (typically as
148 ``backup='.<some extension>'``), it specifies the extension for the backup file,
149 and the backup file remains around; by default, the extension is ``'.bak'`` and
150 it is deleted when the output file is closed. In-place filtering is disabled
151 when standard input is read.
155 The current implementation does not work for MS-DOS 8+3 filesystems.
158 The two following opening hooks are provided by this module:
160 .. function:: hook_compressed(filename, mode)
162 Transparently opens files compressed with gzip and bzip2 (recognized by the
163 extensions ``'.gz'`` and ``'.bz2'``) using the :mod:`gzip` and :mod:`bz2`
164 modules. If the filename extension is not ``'.gz'`` or ``'.bz2'``, the file is
165 opened normally (ie, using :func:`open` without any decompression).
167 Usage example: ``fi = fileinput.FileInput(openhook=fileinput.hook_compressed)``
169 .. versionadded:: 2.5
172 .. function:: hook_encoded(encoding)
174 Returns a hook which opens each file with :func:`codecs.open`, using the given
175 *encoding* to read the file.
177 Usage example: ``fi =
178 fileinput.FileInput(openhook=fileinput.hook_encoded("iso-8859-1"))``
182 With this hook, :class:`FileInput` might return Unicode strings depending on the
183 specified *encoding*.
185 .. versionadded:: 2.5