How do I pipe output from one python script as input to another python script?

Question

For example:

A script1.py gets an infix expression from the user and converts it to a postfix expression and returns it or prints it to stdout

script2.py gets a

Answer 1

For completion's sake, and to offer an alternative to using the os module:

The fileinput module takes care of piping for you, and from running a simple test I believe it'll make it an easy implementation.

To enable your files to support piped input, simply do this:

import fileinput
with fileinput.input() as f_input:  # This gets the piped data for you
    for line in f_input:
        # do stuff with line of piped data

all you'd have to do then is:

$ some_textfile.txt | ./myscript.py

Note that fileinput also enables data input for your scripts like so: $ ./myscript.py some_textfile.txt $ ./myscript.py < some_textfile.txt

This works with python's print output just as easily:

>test.py  # This prints the contents of some_textfile.txt
with open('some_textfile.txt', 'r') as f:
    for line in f:
        print(line)

$ ./test.py | ./myscript.py

Of course, don't forget the hashbang #!/usr/bin/env python at the top of your scripts for this way to work.

The recipe is featured in Beazley & Jones's Python Cookbook - I wholeheartedly recommend it.