How to redirect the raw_input to stderr and not stdout?

Question

I want to redirect the stdout to a file. But This will affect the raw_input. I need to redirect the output of raw_input to stderr instead of stdout. How can I do that?

Answer 1

The only problem with raw_input is that it prints the prompt to stdout. Instead of trying to intercept that, why not just print the prompt yourself, and call raw_input with no prompt, which prints nothing to stdout?

def my_input(prompt=None):
    if prompt:
        sys.stderr.write(str(prompt))
    return raw_input()

And if you want to replace raw_input with this:

import __builtin__
def raw_input(prompt=None):
    if prompt:
        sys.stderr.write(str(prompt))
    return __builtin__.raw_input()

(For more info, see the docs on __builtin__, the module that raw_input and other built-in functions are stored in. You usually don't have to import it, but there's nothing in the docs that guarantees that, so it's better to be safe…)

In Python 3.2+, the module is named builtins instead of __builtin__. (Of course 3.x doesn't have raw_input in the first place, it's been renamed input, but the same idea could be used there.)

Answer 2

Redirect stdout to stderr temporarily, then restore.

import sys

old_raw_input = raw_input
def raw_input(*args):
    old_stdout = sys.stdout
    try:
        sys.stdout = sys.stderr
        return old_raw_input(*args)
    finally:
        sys.stdout = old_stdout