Question

I have a two part question.

>>> class One(object):
...     pass
... 
>>> class Two(object):
...     pass
... 
>>> def digest(constr):
...     c = apply(constr)
...     print c.__class__.__name__
...     print constr.__class__.__name__
... 
>>> digest(Two)
Two
type

How would one create object ‘Two’? Neither constr() or c() work; and it seems that apply turns it into a type.

What happens when you pass a class rather and an instance into a method?

Answer 1

How would one create object ‘Two’?
Neither constr() or c() work; and it
seems that apply turns it into a
type.

The above comment was made in regards to this code:

>>> def digest(constr):
...     c = apply(constr)
...     print c.__class__.__name__
...     print constr.__class__.__name__

apply (deprecated: see @pyfunc’s answer) certainly does not turn the class Two into a type: It already is one.

>>> class Two(object): pass
... 
>>> type(Two)
<type 'type'>

Classes are first class objects: they’re instances of type. This makes sense if you look at the next example.

>>> two = Two()
>>> type(two)
<class '__main__.Two'>

You can see that a class very clearly functions as a type because it can be returned from type. Here’s another example.

>>> Three = type('Three', (Two, ), {'foo': 'bar'})
>>> type(Three)
<type 'type'>
>>> three = Three()
>>> type(three)
<class '__main__.Three'>

You can see that type is a class that can be instantiated. Its constructor takes three arguments: the name of the class, a tuple of base classes and a dictionary containing the class attributes. It returns a new type aka class.

As to your final question,

What happens when you pass a class
rather and an instance into a method?

You’re going to have to be more specific. Classes are just instances of type and so are first class objects. Asking what happens if I pass a class into a method is like asking what happens if I pass an integer into a method: It depends entirely on what the method is expecting.