Should I use a class or dictionary?

Use a dictionary unless you need the extra mechanism of a class. You could also use a namedtuple for a hybrid approach:

>>> from collections import namedtuple
>>> request = namedtuple("Request", "environ request_method url_scheme")
>>> request
<class '__main__.Request'>
>>> request.environ = "foo"
>>> request.environ
'foo'

Performance differences here will be minimal, although I would be surprised if the dictionary wasn't faster.

A class in python is a dict underneath. You do get some overhead with the class behavior, but you won't be able to notice it without a profiler. In this case, I believe you benefit from the class because:

• All your logic lives in a single function
• It is easy to update and stays encapsulated
• If you change anything later, you can easily keep the interface the same