All 15 Command-Line Interfaces (argparse) questions
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How do you create a basic command-line argument parser using argparse? What is the difference between a positional argument and an optional argument (flag) in argparse? How do you specify a default value and a type conversion for an argument? 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 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 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?
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Python › Command-Line Interfaces (argparse)

How do you restrict an argument's accepted values using the 'choices' parameter?

Intermediate

Answer

Pass 'choices=[...]' to restrict the argument to a specific set of allowed values — argparse automatically validates the input against this list and prints a helpful error message listing the valid choices if the user provides something else.
parser.add_argument("--log-level", choices=["debug", "info", "warning", "error"], default="info")
args = parser.parse_args(["--log-level", "invalid"])
# error: argument --log-level: invalid choice: 'invalid' (choose from 'debug', 'info', 'warning', 'error')
Real-world example Restricting a --log-level or --format flag to a specific, known set of valid string values.

Common follow-ups: Can 'choices' be combined with 'type=int' to restrict to a specific set of allowed NUMBERS instead of strings?

Data Types & Structures
All 15 Command-Line Interfaces (argparse) questions