11.2 fileinput -- Iterate over lines from multiple input streams
This module implements a helper class and functions to quickly write a loop over standard input or a list of files.
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 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 input() or FileInput(). If an I/O error occurs during opening or reading a file, 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.
It is possible that the last line of a file does not end in a newline character; lines are returned including the trailing newline when it is present.
You can control how files are opened by providing an opening hook via the openhook parameter to input() or 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:
-
Create an instance of the 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
FileInput class.
Changed in version 2.5: Added the mode and openhook parameters.
The following functions use the global state created by input(); if there is no active state, RuntimeError is raised.
-
Return the name of the file currently being read. Before the first
line has been read, returns
None.
-
Return the integer ``file descriptor'' for the current file. When no
file is opened (before the first line and between files), returns
-1. New in version 2.5.
-
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.
-
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.
- Returns true if the line just read is the first line of its file, otherwise returns false.
-
Returns true if the last line was read from
sys.stdin, otherwise returns false.
- 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.
- Close the sequence.
The class which implements the sequence behavior provided by the module is available for subclassing as well:
-
Class FileInput is the implementation; its methods
filename(), fileno(), lineno(),
fileline(), isfirstline(), isstdin(),
nextfile() and close() correspond to the functions
of the same name in the module.
In addition it has a readline() method which
returns the next input line, and a __getitem__() method
which implements the sequence behavior. The sequence must be
accessed in strictly sequential order; random access and
readline() cannot be mixed.
With mode you can specify which file mode will be passed to 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.
Changed in version 2.5: Added the mode and openhook parameters.
Optional in-place filtering: if the keyword argument
inplace=1 is passed to input() or to the
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 keyword argument backup='.<some
extension>' is also given, 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.
Caveat: The current implementation does not work for MS-DOS 8+3 filesystems.
The two following opening hooks are provided by this module:
-
Transparently opens files compressed with gzip and bzip2 (recognized
by the extensions
'.gz'and'.bz2') using the gzip and bz2 modules. If the filename extension is not'.gz'or'.bz2', the file is opened normally (ie, using open() without any decompression).Usage example: "fi = fileinput.FileInput(openhook=fileinput.hook_compressed)"
New in version 2.5.
-
Returns a hook which opens each file with 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, FileInput might return Unicode strings depending on the specified encoding. New in version 2.5.
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Release 2.5, documentation updated on 19th September, 2006.