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

Beginner

Answer

A positional argument is REQUIRED and identified by its ORDER on the command line (declared without a leading dash); an optional argument is identified by a FLAG name (starting with '-' or '--') and is optional by default unless you explicitly mark it 'required=True'.
parser.add_argument("filename")               # positional: required, identified by position
parser.add_argument("--verbose", action="store_true")  # optional: identified by --verbose flag

# python script.py data.txt --verbose
Real-world example Requiring a filename as a positional argument while making a --verbose logging flag optional.

Common follow-ups: How would you make an optional-looking flag (like --output) actually REQUIRED?

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