Python · OS, sys, argparse & subprocess

What does `r.stdout` hold after this, and why is `text=True` important? ``` r = subprocess.run( ["echo", "hi"], capture_output=True, text=True) ```

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More in OS, sys, argparse & subprocess

You run an external tool with subprocess.run(["mytool", "--check"]). It fails (exit code 1) but your Python script keeps going as if nothing happened. How do you make the failure raise?

What are sys.stdin, sys.stdout, and sys.stderr, and why send error/diagnostic messages to stderr rather than stdout?

You read a config value with os.environ["API_KEY"]. It works on your machine but crashes with KeyError on a fresh deploy where the var isn't set. What's the safe way to read it?

What does this print when run as `python prog.py hello`? ``` import sys print(len(sys.argv)) print(sys.argv[0]) ```

A script is called `python add.py 2 3` with this body. What does it print? ``` import sys print(sys.argv[1] + sys.argv[2]) ```

Why reach for argparse instead of just reading sys.argv yourself for a CLI that takes a couple of flags and arguments?

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