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:
for line in fileinput.input():
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
All files are opened in text mode. 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
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
The following functions use the global state created by
input(); if there is no active state,
RuntimeError is raised.
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.
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.
Class FileInput is the implementation; its methods
filename(), 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.
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