How do I detect whether sys.stdout is attached to terminal or not?

Is there a way to detect whether sys.stdout is attached to a console terminal or not? For example, I want to be able to detect if foo.py is run via:

$ python foo.py  # user types this on console

OR

$ python foo.py > output.txt # redirection
$ python foo.py | grep ....  # pipe

The reason I ask this question is that I want to make sure that my progressbar display happens only in the former case (real console).

Answers:

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Method 1

This can be detected using isatty:

if sys.stdout.isatty():
    # You're running in a real terminal
else:
    # You're being piped or redirected

To demonstrate this in a shell:

• python -c "import sys; print(sys.stdout.isatty())" should write True
• python -c "import sys; print(sys.stdout.isatty())" | cat should write False

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