You want a script you’ve written to be able to accept input using whatever mechanism

is easiest for the user. This should include piping output from a command to the script,

redirecting a file into the script, or just passing a filename, or list of filenames, to the

script on the command line.

Python’s built-in fileinput module makes this very simple and concise. If you have a

script that looks like this:

#!/usr/bin/env python3

import fileinput

with fileinput.input() as f_input:

for line in f_input:

print(line, end='')

Then you can already accept input to the script in all of the previously mentioned ways.

If you save this script as filein.py and make it executable, you can do all of the following

and get the expected output:

$ ls | ./filein.py # Prints a directory listing to stdout.

$ ./filein.py /etc/passwd # Reads /etc/passwd to stdout.

$ ./filein.py < /etc/passwd # Reads /etc/passwd to stdout.

The fileinput.input() function creates and returns an instance of the FileInput

class. In addition to containing a few handy helper methods, the instance can also be

used as a context manager. So, to put all of this together, if we wrote a script that expected

to be printing output from several files at once, we might have it include the filename

and line number in the output, like this:

>>> import fileinput

>>> with fileinput.input('/etc/passwd') as f:

>>> for line in f:

... print(f.filename(), f.lineno(), line, end='')

...

<other output omitted>

Using it as a context manager ensures that the file is closed when it’s no longer being

used, and we leveraged a few handy FileInput helper methods here to get some extra

information in the output.