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

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