All 15 Command-Line Interfaces (argparse) questions
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How do you restrict an argument's accepted values using the 'choices' parameter? How do you accept a variable number of arguments for a single flag, like a list of filenames? How do you implement boolean flags using action='store_true' and action='store_false'? How do you provide a short and a long form for the same flag, like -v and --verbose? How do you group related arguments visually in the generated --help output using argument groups? How do you implement mutually exclusive arguments, where the user must choose EXACTLY ONE of a set of flags? How do you write a custom 'type=' validation function for argparse that raises a properly-formatted error for invalid input? How would you build a CLI tool where some arguments can also be set via environment variables, falling back to a default if neither is provided? How do you customize argparse's automatically-generated usage and help text formatting, like preserving specific line breaks in the description? How would you write integration tests for an argparse-based CLI tool using pytest, verifying both successful parsing and expected error behavior?
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How do you implement subcommands (like 'git commit' or 'git push') using argparse's add_subparsers()?

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Answer

Call add_subparsers() on the main parser to create a subparser group, then add each subcommand as its own separate ArgumentParser (via add_parser()) with its own specific arguments — each subcommand's parsed arguments merge into the same top-level Namespace, distinguished by a 'dest' attribute indicating which subcommand was invoked.
parser = argparse.ArgumentParser(prog="mytool")
subparsers = parser.add_subparsers(dest="command", required=True)

push_parser = subparsers.add_parser("push")
push_parser.add_argument("remote")

commit_parser = subparsers.add_parser("commit")
commit_parser.add_argument("-m", "--message", required=True)

args = parser.parse_args(["commit", "-m", "Initial commit"])
print(args.command, args.message)  # commit Initial commit
Real-world example Building a multi-command CLI tool like a custom deployment or database migration utility with distinct subcommands, each with its own arguments.

Common follow-ups: How would you dispatch to a different handler FUNCTION based on which subcommand (args.command) was actually invoked?

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All 15 Command-Line Interfaces (argparse) questions