what is the right way to treat Python argparse.Namespace() as a dictionary?

Question

If I want to use the results of argparse.ArgumentParser(), which is a Namespace object, with a method that expects a dictionary or mapping-like obj

Answer 1

Is it proper to "reach into" an object and use its dict property?

In general, I would say "no". However Namespace has struck me as over-engineered, possibly from when classes couldn't inherit from built-in types.

On the other hand, Namespace does present a task-oriented approach to argparse, and I can't think of a situation that would call for grabbing the __dict__, but the limits of my imagination are not the same as yours.

Answer 2

Straight from the horse's mouth:

If you prefer to have dict-like view of the attributes, you can use the standard Python idiom, vars():

>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo')
>>> args = parser.parse_args(['--foo', 'BAR'])
>>> vars(args)
{'foo': 'BAR'}

— The Python Standard Library, 16.4.4.6. The Namespace object

Answer 3

You can access the namespace's dictionary with vars():

>>> import argparse
>>> args = argparse.Namespace()
>>> args.foo = 1
>>> args.bar = [1,2,3]
>>> d = vars(args)
>>> d
{'foo': 1, 'bar': [1, 2, 3]}

You can modify the dictionary directly if you wish:

>>> d['baz'] = 'store me'
>>> args.baz
'store me'

Yes, it is okay to access the __dict__ attribute. It is a well-defined, tested, and guaranteed behavior.