How to determine if IO redirection is occurring with the output from a Python program?

[Chris Angelico]

On Wed, Apr 18, 2012 at 12:21 AM, Edward d'Auvergne
<edward at nmr-relax.com> wrote:
> I was wondering if anyone knows of how to detect when IO redirection
> of any form is happening within a Python program?  I would like to
> emulate the behaviour of the GNU tools (for example the Unix commands
> 'ls' or 'grep') whereby ascii escape sequences are printed if the
> output is solely to the terminal, and in all other cases (redirection
> to file via '>', pipes via '|', or more complex redirections) the
> ascii escape characters are suppressed.  Any ideas would be
> appreciated!

What you want is the "is-a-TTY" query, which is available in Python as
a method on the file-like object:

import sys
if sys.stdout.isatty(): # True if console, False if redirected
    # do your fancy escape character stuff

Tip: Like the GNU tools, make this only a default. For instance, both
ls and grep have an option --color=WHEN where WHEN is either "never",
"always", or "auto". If you choose auto (which you can make the
default), the tools then check if stdout is a TTY.

ChrisA