The fileinput module

This module allows you to loop over the contents of one or more text files.

Example: Using the fileinput module to loop over a text file

# File: fileinput-example-1.py

import fileinput
import sys

for line in fileinput.input("samples/sample.txt"):
    sys.stdout.write("-> ")
    sys.stdout.write(line)

-> We will perhaps eventually be writing only small
-> modules which are identified by name as they are
-> used to build larger ones, so that devices like
-> indentation, rather than delimiters, might become
-> feasible for expressing local structure in the
-> source language.
->      -- Donald E. Knuth, December 1974

You can pass in a single filename, or a list of filenames. If you leave out the filename argument, fileinput gets the names from sys.argv.

The module also allows you to get metainformation about the current line. This includes isfirstline, filename, and lineno:

Example: Using the fileinput module to process multiple files

# File: fileinput-example-2.py

import fileinput
import glob
import string, sys

for line in fileinput.input(glob.glob("samples/*.txt")):
    if fileinput.isfirstline(): # first in a file?
        sys.stderr.write("-- reading %s --\n" % fileinput.filename())
    sys.stdout.write(str(fileinput.lineno()) + " " + string.upper(line))

-- reading samples\sample.txt --
1 WE WILL PERHAPS EVENTUALLY BE WRITING ONLY SMALL
2 MODULES WHICH ARE IDENTIFIED BY NAME AS THEY ARE
3 USED TO BUILD LARGER ONES, SO THAT DEVICES LIKE
4 INDENTATION, RATHER THAN DELIMITERS, MIGHT BECOME
5 FEASIBLE FOR EXPRESSING LOCAL STRUCTURE IN THE
6 SOURCE LANGUAGE.
7    -- DONALD E. KNUTH, DECEMBER 1974

Processing text files in place is also easy. Just call the input function with the inplace keyword argument set to 1, and the module takes care of the rest.

Example: Using the fileinput module to convert CRLF to LF

# File: fileinput-example-3.py

import fileinput, sys

for line in fileinput.input(inplace=1):
    # convert Windows/DOS text files to Unix files
    if line[-2:] == "\r\n":
        line = line[:-2] + "\n"
    sys.stdout.write(line)

[comment on/vote for this article]

Comment:

My provider is learning Python and trying to duplicate his old PowerBASIC console program. There are two new options in the fileinput.input() in version 2.5 of mode and openhook. How about an example that shows how to use the openhook? I suggest using glob so say all the *.txt files in the \input directory are transformed by {string manipulation block} and placed in the \output directory. If Mr Tunacan does not figure this out soon I'm going to pee on his keyboard, because this is taking way too long.

Posted by Kitty Poo (2006-10-30)

Comment:

It looks like example fileinput-example-3.py is lacking a file name when it calls input(inplace=1). In fact, according to fileinput's doc, "in-place filtering is disabled when standard input is read."

Posted by Eric-Olivier LE BIGOT (EOL) (2006-10-30)

If you don't pass in a filename, fileinput uses sys.argv /F