[New-bugs-announce] [issue16399] argparse:

[Markus Amalthea Magnuson]

New submission from Markus Amalthea Magnuson:

If the default value for a flag is a list, and the action append is used, argparse doesn't seem to override the default, but instead adding to it. I did this test script:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument(
    '--foo',
    action='append',
    default=['bar1', 'bar2']
)
args = parser.parse_args()

print args.foo

Output is as follows:

$ ./argparse_foo_test.py
['bar1', 'bar2']

$ ./argparse_foo_test.py --foo bar3
['bar1', 'bar2', 'bar3']

I would expect the last output to be ['bar3'].

Is this on purpose (although very confusing) or is it a bug?

----------
components: Library (Lib)
files: argparse_foo_test.py
messages: 174735
nosy: Markus.Amalthea.Magnuson
priority: normal
severity: normal
status: open
title: argparse:
type: behavior
versions: Python 2.7
Added file: http://bugs.python.org/file27874/argparse_foo_test.py

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16399>
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