11.3. fileinput
— Iterate over lines from multiple input streams¶
Source code: 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 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
. 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,
OSError
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 fileinput.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:
-
fileinput.
input
(files=None, inplace=False, backup='', bufsize=0, mode='r', openhook=None)¶ 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 theFileInput
class.The
FileInput
instance can be used as a context manager in thewith
statement. In this example, input is closed after thewith
statement is exited, even if an exception occurs:with fileinput.input(files=('spam.txt', 'eggs.txt')) as f: for line in f: process(line)
Distinto en la versión 3.2: Can be used as a context manager.
Distinto en la versión 3.5.2: The bufsize parameter is no longer used.
The following functions use the global state created by fileinput.input()
;
if there is no active state, RuntimeError
is raised.
-
fileinput.
filename
()¶ Return the name of the file currently being read. Before the first line has been read, returns
None
.
-
fileinput.
fileno
()¶ Return the integer «file descriptor» for the current file. When no file is opened (before the first line and between files), returns
-1
.
-
fileinput.
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.
-
fileinput.
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.
-
fileinput.
isfirstline
()¶ Returns true if the line just read is the first line of its file, otherwise returns false.
-
fileinput.
isstdin
()¶ Returns true if the last line was read from
sys.stdin
, otherwise returns false.
-
fileinput.
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.
-
fileinput.
close
()¶ Close the sequence.
The class which implements the sequence behavior provided by the module is available for subclassing as well:
-
class
fileinput.
FileInput
(files=None, inplace=False, backup='', bufsize=0, mode='r', openhook=None)¶ Class
FileInput
is the implementation; its methodsfilename()
,fileno()
,lineno()
,filelineno()
,isfirstline()
,isstdin()
,nextfile()
andclose()
correspond to the functions of the same name in the module. In addition it has areadline()
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 andreadline()
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.
A
FileInput
instance can be used as a context manager in thewith
statement. In this example, input is closed after thewith
statement is exited, even if an exception occurs:with FileInput(files=('spam.txt', 'eggs.txt')) as input: process(input)
Distinto en la versión 3.2: Can be used as a context manager.
Obsoleto desde la versión 3.4: The
'rU'
and'U'
modes.Distinto en la versión 3.5.2: The bufsize parameter is no longer used.
Optional in-place filtering: if the keyword argument inplace=True
is
passed to fileinput.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 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:
-
fileinput.
hook_compressed
(filename, mode)¶ Transparently opens files compressed with gzip and bzip2 (recognized by the extensions
'.gz'
and'.bz2'
) using thegzip
andbz2
modules. If the filename extension is not'.gz'
or'.bz2'
, the file is opened normally (ie, usingopen()
without any decompression).Usage example:
fi = fileinput.FileInput(openhook=fileinput.hook_compressed)