Namespaces within a Python Class

问题:

I have this:

class MyClass:
    """A simple example class"""
    i = 12345
    def f(self):
        print i                     # self.i will work just fine
        return 'hello world'

When I do:

>>> x = MyClass()
>>> 
>>> x.f()

I get an error, as expected.

My question is:

1. Why do I get the error?

2. Why is there no namespace between the namespace of the function(or method) definition and the global namespace of the module containing the class?

3. Is there any other way to reference i inside f in this case other than using self?

回答1:

1. You've got an error because print i is trying to print a global (for the module) variable i. If you want to use the member of the class you should write self.i.
2. Because Guido Van Rossum decided not to use namespaces. Actually, I don't know how to answer anymore.
3. Yes, but no. Yes, because you can use "reflection" (I can't remember how it is called in python) and access any member of the class. No, because using self is the only usable way.