What's the best way to tell if a Python program has anything to read from stdin?

Question

I want a program to do one thing if executed like this:

cat something | my_program.py

and do another thing if run like this

Answer 1

If you want to detect if someone is piping data into your program, or running it interactively you can use isatty to see if stdin is a terminal:

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