Documentation

The documentation for set_defaults() in the argparse module states:

Note that parser-level defaults always override argument-level defaults

And gives the following snippet:

>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', default='bar')
>>> parser.set_defaults(foo='spam')
>>> parser.parse_args([])
Namespace(foo='spam')

However, swapping the order of add_argument() and set_defaults() gives a different result:

>>> parser = argparse.ArgumentParser()
>>> parser.set_defaults(foo='spam')
>>> parser.add_argument('--foo', default='bar')
>>> parser.parse_args([])
Namespace(foo='bar')

To me, the statement in the documentation implies that parser-level defaults take precedence over argument-level defaults, but that is not the case. In fact, they overwrite one another, and order is important.

Linked PRs

• GH-108009: Add clarification of parser and argument defaults in argparse docs #124154