All 15 Command-Line Interfaces (argparse) questions
More in Command-Line Interfaces (argparse)
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 implement subcommands (like 'git commit' or 'git push') using argparse's add_subparsers()? How do you group related arguments visually in the generated --help output using argument groups? 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? How do you build a plugin-style CLI where subcommands are dynamically discovered and registered from separate modules, rather than hardcoded?
Advertisement
Back to results for “Set”
Python › Command-Line Interfaces (argparse)

How do you implement mutually exclusive arguments, where the user must choose EXACTLY ONE of a set of flags?

Advanced

Answer

add_mutually_exclusive_group() creates a group where argparse automatically raises an error if the user provides MORE THAN ONE of the group's arguments together; pass 'required=True' to the group to also enforce that AT LEAST ONE must be provided.
group = parser.add_mutually_exclusive_group(required=True)
group.add_argument("--verbose", action="store_true")
group.add_argument("--quiet", action="store_true")
# python script.py --verbose --quiet
# error: argument --quiet: not allowed with argument --verbose
Real-world example Enforcing that a CLI tool's output mode is EXACTLY one of --verbose, --quiet, or --normal, never a combination.

Common follow-ups: Can a mutually exclusive group contain MORE than two arguments?

Exception Handling
All 15 Command-Line Interfaces (argparse) questions