How can you pass a list of arguments to a command-line program using argparse?

Passing Lists as Command-Line Arguments with argparse

When building command-line programs, it's often beneficial to allow users to pass lists as arguments. argparse makes this possible, providing several options to accomplish this.

nargs

To receive a list of arguments, utilize the 'nargs' parameter. Specify ' ' to accept one or more arguments, '*' to accept zero or more, '?' to accept zero or one, or a specific number (like 2) to accept that exact number of arguments.

parser = argparse.ArgumentParser()<br>parser.add_argument('-l', '--list', nargs=' ')<br>

This approach makes it easy for users to provide multiple arguments as a single input.

append

Alternatively, you can use the 'append' action to append each argument to a list as it is encountered.

parser.add_argument('-l', '--list', action='append')<br>

This method requires users to specify the flag multiple times, one for each argument they want to include in the list.

Avoid type=list

While it may seem intuitive to set 'type' to 'list,' this is not recommended as it returns a list of lists, not a flattened list. This can lead to unexpected behavior.

Example Usage

Consider a script where the user needs to pass a list of integers.

parser = argparse.ArgumentParser()<br>parser.add_argument('-l', '--list', nargs=' ', type=int)<br>

This allows the user to enter multiple integers, which are then automatically converted to a list of integers and stored in the 'list' variable.

Note:

• Avoid using quotes on the command line as they can interfere with argparse's parsing.


• Don't use type=list, as it leads to a list of lists instead of a flattened list.

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