python argparse option string not complete but value is assigned

Question

Argparse doesn't seem to check for entire string of option to assign the value. Is this a bug or intended one? What are the use cases for this if this is intended?

Run the following program using python3 test.py -test "testing"

import argparse
if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('-testurl', dest='testurl')
    args = parser.parse_args()
    print(args)

Output is

Namespace(testurl='testing')

Answer 1

We can use double dash (--) in options and make allow_abbrev=False in parser to force the exact argument to be parsed [reference: argument parser documentation]:

import argparse
if __name__ == '__main__':
    parser = argparse.ArgumentParser(allow_abbrev=False)
    parser.add_argument('--testurl', dest='testurl')
    args = parser.parse_args()
    print(args)

Output:

> python3 df_reg.py --test "testing" 
usage: df_reg.py [-h] [--testurl TESTURL]
df_reg.py: error: unrecognized arguments: --test testing

> python3 df_reg.py --testurl "testing"
Namespace(testurl='testing')

References:

• Argument parser documentation