Does type create the class 'Object' in python

Question

I was reading about this excellent post on metaclasses What is a metaclass in Python?. The accepted answer shows how to create a class using type with the following signature.

type(name of the class, 
      tuple of the parent class (for inheritance, can be empty), 
      dictionary containing attributes names and values)

That makes me wonder who creates the object class. Is object class also created by type class?

pssst, Karthick: join http://bostonpython.com , if you haven't already... — Ned Batchelder, Jun 25 '12 at 20:26

score 6 · Accepted Answer · answered Jun 25 '12 at 20:07

6

In theory you are correct. object is an instance of type. But, when you check type's base classes, you'll find that type inherits from object! How can this be?

The truth is, this is hard-coded in the Python interpreter. Both object and type are given; neither is actually involved in any way with creating the other.

answered Jun 25 '12 at 20:07

kindall

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Exactly.. type inherits from object and object is instantiated by type.. How is this possible and hence this question! – Karthick Jun 25 '12 at 20:09
2

@Jon: `type.__mro__ == (, )`. Also `issubclass(type, object) == True`. – kindall Jun 25 '12 at 20:09
What version Python are we using here? – Jon Clements Jun 25 '12 at 20:21
Got the above results in both Python 2.6.6 and 3.1.2. – kindall Jun 25 '12 at 20:55

score 3 · Answer 2 · answered Jun 25 '12 at 20:30

The main thing to remember at these rarified levels of the object/type hierarchy is that things like object and type are not created in .py files at all, they are created statically in C code, along with the rest of the foundational underpinnings of CPython. So they aren't necessarily "created" with any particular Python code.

score 0 · Answer 3 · answered Jun 25 '12 at 20:13

type is a bit of a - umm, not sure how to describe it - weirdo of the language.

It can be used to do type(someobj) or used as a constructor (with 3 params) of some sorts to create new types derived from a base with instances. As you have seen with meta-classes - it's useful to make factory classes - although, IMHO unless you really want to be too clever, using class decorators makes this slightly easier in 2.6+

Does type create the class 'Object' in python

3 Answers3