How to receive command line arguments in Python

What are command line arguments?

A command line argument is a character string specified when starting a program from the command input screen (command line) of a computer. Also, the value of the variable etc. that received this on the program side.

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Command line arguments are the arguments of the main function. You can give values to command line arguments from the command line when you run it.

http://www.ritsumei.ac.jp/~mmr14135/johoWeb/cmnds.html

>>> ls -a
↑ here

Receive command line arguments in Python

There are three main ways to receive command line arguments in Python.

1. Use sys.argv
2. Use ʻargparse`
3. Use click

is.

sys.argv

This is the most recognized (I think) method. Get it using sys, the Python standard library.

args.py

import sys


def main() -> None:
    args = sys.argv
    print(args)


if __name__=='__main__':
    main()

Run

>>> python args.py aaa 123 hoge
['args.py', 'aaa', '123', 'hoge']

argparse

A Python standard library dedicated to command line arguments. You can specify the Help function and type. There is a habit of handling.

args2.py

import argparse


def main() -> None:
    parser = argparse.ArgumentParser(description='Description')

    parser.add_argument('description', help='Argument description')  #If not specified at runtime, an error will occur.
    parser.add_argument('hoge', help='hogehoge')  #The order is fixed.
    parser.add_argument('--foo', help='option')  #1 hyphen~If you attach two, you do not have to specify it at runtime.

    args = parser.parse_args()

    print(args.description)
    print(args.hoge)
    print(args.foo)


if __name__ == "__main__":
    main()

Run

>>> python args2.py -h
usage: aaa.py [-h] [--foo FOO] description hoge

Description

positional arguments:
description Argument description
  hoge         hogehoge

optional arguments:
  -h, --help   show this help message and exit
  --foo FOO    option

>>> python args2.py aaa bbb
aaa
bbb
None

>>> python args2.py aaa bbb --foo 123
aaa
bbb
123

click

Python command line parser. In other words, a module for command line analysis. Since it is not a Python standard library, it needs to be installed separately, but the above two are omitted for ease of understanding and usability. Therefore, it is OK if you remember this By the way, click, Flask, and jinja are same project.

#Installation
pip install click

args3.py

import click


@click.command()
@click.option('--args', prompt=True, help='Description')
@click.option('--hoge', prompt=True, is_flag=True, help='hogehoge')
def main(args: str, hoge: bool) -> None:
    if hoge:
        print(args)


if __name__ == "__main__":
    main()

Run

>>> python args3.py --args foo --hoge
foo

>>> python args3.py
Args: aaaaa
Hoge [y/N]: y
aaaaa

Reference material

How to handle command line arguments in Python (sys.argv, argparse) [How to pass command line arguments in Python](https://intellectual-curiosity.tokyo/2018/12/14/python%E3%81%A7%E3%82%B3%E3%83%9E%E3%83 % B3% E3% 83% 89% E3% 83% A9% E3% 82% A4% E3% 83% B3% E5% BC% 95% E6% 95% B0% E3% 82% 92% E6% B8% A1 % E3% 81% 99% E6% 96% B9% E6% B3% 95 /) A brief summary of how to use ArgumentParser Python: Click on the command line parser was too convenient