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 object (see collections.Mapping), what is the right way to do it?

C:\>python Python 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit (Intel)] on win 32 Type "help", "copyright", "credits" or "license" for more information. >>> import argparse >>> args = argparse.Namespace() >>> args.foo = 1 >>> args.bar = [1,2,3] >>> args.baz = 'yippee' >>> args['baz'] Traceback (most recent call last):   File "<stdin>", line 1, in <module> TypeError: 'Namespace' object has no attribute '__getitem__' >>> dir(args) ['__class__', '__contains__', '__delattr__', '__dict__', '__doc__', '__eq__', '_ _format__', '__getattribute__', '__hash__', '__init__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__ ', '__str__', '__subclasshook__', '__weakref__', '_get_args', '_get_kwargs', 'ba r', 'baz', 'foo'] 

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

I would think the answer is no: __dict__ smells like a convention for implementation, but not for an interface, the way __getattribute__ or __setattr__ or __contains__ seem to be.

Answer 1

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.