How to Handle Lists as Command-Line Arguments with argparse in Python?

Handling Lists as Command-Line Arguments with argparse

In Python, the argparse module facilitates the parsing of command-line arguments. When working with lists as arguments, it's crucial to understand the appropriate options.

nargs

One method is to utilize nargs, which specifies the number of arguments accepted for an option. By default, nargs=1 accepts a single argument. However, using nargs=' ' or nargs='*' allows multiple arguments.

<code class="python">parser.add_argument('-l', '--list', nargs='+', help='Set flag')</code>

action='append'

Another alternative is action='append'. This approach appends each encountered argument to a list instead of collecting them in a single argument.

<code class="python">parser.add_argument('-l', '--list', action='append', help='Set flag')</code>

Avoid type=list

In contrast, using type=list is generally inadvisable with argparse. It interprets each argument as a list, resulting in a list of lists.

Demonstration

The provided code demonstrates the use of these options:

<code class="python">import argparse

parser = argparse.ArgumentParser()

# Demonstration with nargs
parser.add_argument('--nargs', nargs='+')

# Demonstration with action='append'
parser.add_argument('--append-action', action='append')

for _, value in parser.parse_args()._get_kwargs():
    if value is not None:
        print(value)</code>

Output:

Assuming the script is invoked with python arg.py --nargs 1234 2345 3456 4567, the output with nargs will be:

['1234', '2345', '3456', '4567']

Alternatively, invoking the script with python arg.py --append-action 1234 --append-action 2345 --append-action 3456 --append-action 4567 will produce:

['1234', '2345', '3456', '4567']

Guidelines

• For straightforward user interactions, consider nargs.
• Action='append' is preferred when arguments can be mixed with positional arguments, or when the exact number of arguments is not predetermined.
• Avoid using type=list as it leads to undesired list-of-lists structures.

The above is the detailed content of How to Handle Lists as Command-Line Arguments with argparse in Python?. For more information, please follow other related articles on the PHP Chinese website!