When we are using python to develop the backend program, we usually use argparse package to pass some arguments to python program, then we a write a shell script to make our program to be a pipeline.
Today, I want to record how to pass a List data, If we used the following program (named test.py) to pass arguments:
# coding: utf-8 import argparse # Argument parser = argparse.ArgumentParser() parser.add_argument('--list_data', type=int) args = parser.parse_args() print('Results:', args.list_data)
Then I use the following command via terminal:
python3 test.py --list_data 1 2 3 4 5
Output:
usage: test.py [-h] [--list_data LIST_DATA]
test.py: error: unrecognized arguments: 2 3 4 5We will got these error message.
How To Pass “List” Data
Basically, just add a parameter like nargs="+" to add_argument(). But still be careful, set the type of the specified data type to List.
The following is the correct demonstration:
# coding: utf-8 import argparse # Argument parser = argparse.ArgumentParser() parser.add_argument('--list_data', type=int, nargs='+') args = parser.parse_args() print('Results:', args.list_data)
Then use the following command:
python3 test.py --list_data 1 2 3 4 5Output:
Results: [1, 2, 3, 4, 5]On the contrary, what if we set type=list easily? (…I did it at the beginning)
# coding: utf-8 import argparse # Argument parser = argparse.ArgumentParser() parser.add_argument('--list_data', type=list, nargs='+') args = parser.parse_args() print('Results:', args.list_data)
Then enter the following command:
python3 test.py --list_data 1 2 3 4 5Output:
Results: [['1'], ['2'], ['3'], ['4'], ['5']]That’s right, all the elements in the list have also become the data type of the List! I think this should not be the desired result.
References
- https://docs.python.org/3/library/argparse.html
- https://stackoverflow.com/questions/15753701/how-can-i-pass-a-list-as-a-command-line-argument-with-argparse
- https://www.kite.com/python/answers/how-to-pass-a-list-as-an-argument-using-argparse-in-python