Argparse argument names with _ in name can be parsed incorrectly and take invalid options.

[flyingaceaaa]

Bug description:

When using argparse library and adding arguments, having an argument name such as --my_arg can result in python interpreting any matching --my argument passed to command line to be viewed as --my_arg.

For Example, if I call my file below with the following argument, it will not error even though --model is not a valid argument created in parser, but --model_path is.

<python_version> test_arg_error.py --model /some/arbitrary/path

python file name: test_arg_error.py

import argparse 
parser = argparse.ArgumentParser(description=" Argparse Error Description")
parser.add_argument("--model_path")
args = parser.parse_args()

CPython versions tested on:

3.10, 3.9

Operating systems tested on:

Linux

[donBarbos]

Sorry, but the documentation already answers this question.

And you can disable it using argument allow_abbrev=False

[donBarbos]

Example

test.py:

import argparse
parser = argparse.ArgumentParser(description=" Argparse Error Description", allow_abbrev=False)
parser.add_argument("--model_path")
args = parser.parse_args()

output:

$ python test.py --model /some/arbitrary/path
usage: test.py [-h] [--model_path MODEL_PATH]
test.py: error: unrecognized arguments: --model /some/arbitrary/path

[donBarbos]

@terryjreedy looks like it can be closed ;-)