How to tell if python script is being run in a terminal or via GUI?

Question

I'm working in Linux and am wondering how to have python tell whether it is being run directly from a terminal or via a GUI (like alt-F2) where output will need to be sent to a window rather than stdout which will appear in a terminal.

In bash, this done by:

if [ -t 0 ] ; then  
    echo "I'm in a terminal"
else
    zenity --info --title "Hello" --text "I'm being run without a terminal"
fi

How can this be accomplished in python? In other words, the equivalent of [ -t 0 ])?

Answer 1

$ echo ciao | python -c 'import sys; print sys.stdin.isatty()'
False

Of course, your GUI-based IDE might choose to "fool" you by opening a pseudo-terminal instead (you can do it yourself to other programs with pexpect, and, what's sauce for the goose...!-), in which case isatty or any other within-Python approach cannot tell the difference. But the same trick would also "fool" your example bash program (in exactly the same way) so I guess you're aware of that. OTOH, this will make it impossible for the program to accept input via a normal Unix "pipe"!

A more reliable approach might therefore be to explicitly tell the program whether it must output to stdout or where else, e.g. with a command-line flag.

Answer 2

I scoured SE for an answer to this but everywhere indicated the use of sys.stdout.isatty() or os.isatty(sys.stdout.fileno()). Neither of these dependably caught my GUI test cases.

Testing standard input was the only thing that worked for me:

sys.stdin.isatty()