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Nargs

As explained in Tiny Python Projects: Learn coding and testing with puzzles and games

nargs is an argparse argument-definition parameter that specifies how many command-line values an argument accepts.

nargs is an argparse parameter that controls how many command-line values an argument accepts. It lets a program require one or more values, permit zero or more, or accept an optional value. section 6.5

Use these common nargs values:

Accepting picnic items

Define a positional argument with `nargs='+'` when the program needs at least one item: `parser.add_argument('item', nargs='+', help='Item(s) to bring')` With no item, argparse reports an error; with `chips`, the program receives the supplied item. section 3.1

Reading optional file inputs

Use `nargs='*'` for zero or more files. Combined with `type=argparse.FileType('rt')` and `default=[sys.stdin]`, the program can process named readable files or standard input. section 6.3.1

Table 6.1 Possible values for nargs (view table figure)

Symbol

Meaning

?

Zero or one

*

Zero or more

+

One or more

Use the table to compare the three symbolic nargs values and their accepted argument counts. section 6.1.1

How Tiny Python Projects: Learn coding and testing with puzzles and games covers it

How deep it goes
Explains ?, *, and + through argument definitions, usage output, defaults, and resulting input collections.
Examples
Uses picnic items, word-count file inputs, and Mad Libs substitution strings as concrete multi-value arguments.
What it assumes
Assumes basic Python command-line and argparse argument definitions while demonstrating defaults and validation.
What you can do after
Apply it via argparse to constrain positional or optional inputs and handle zero-or-more or one-or-more values.
How it connects
Connects argparse argument counts with positional arguments, optional arguments, readable file arguments, default values, and sys.stdin.
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