Brandon Rozek

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PhD Student @ RPI studying Automated Reasoning in AI and Linux Enthusiast.

Python Argument Parser

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For a much better description of argument parsing in Python, please visit https://docs.python.org/3/library/argparse.html.

I’m creating this post because even though it’s not too complicated, I keep forgetting how to do argument parsing in Python. I also tricked myself into thinking each time that I already wrote a blog post on this. Let’s correct this once and for all and include a quick example!

import argparse
parser = argparse.ArgumentParser(description="Description to show in help")
parser.add_argument("pos_arg1", type=str, help="Required positional argument")
parser.add_argument("--flag1", type=str, help="Optional flag argument")
parser.add_argument("--flag2", type=int, required=True, help="Required flag argument")
parser.add_argument("--flag3", type=int, default=0, help="Optional flag argument \
    with default value of 0")
args = vars(parser.parse_args())

Now if you call the program with no arguments you’ll get the following message:

usage: testarg.py [-h] [--flag1 FLAG1] --flag2 FLAG2 pos_arg1
testarg.py: error: the following arguments are required: pos_arg1, --flag2

This comes with a built in -h as well!

usage: testarg.py [-h] [--flag1 FLAG1] --flag2 FLAG2 pos_arg1

Description to show in help

positional arguments:
  pos_arg1       Required positional argument

optional arguments:
  -h, --help            show this help message and exit
  --flag1 FLAG1         Optional flag argument
  --flag2 FLAG2         Required flag argument

Within the code you can parse the argument names by accessing the args dictionary.

pos_arg1 = args['pos_arg1']
flag1 = args['flag1']
flag2 = args['flag2']
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