How is True < 2 implemented?

Question

It's not implemented directly on bool.

>>> True.__lt__(2) AttributeError: 'bool' object has no attribute '__lt__' 

And it's apparently not implemented on int either:

>>> super(bool, True).__lt__(2) AttributeError: 'super' object has no attribute '__lt__' 

There is no reflected version of __lt__ for 2 to control the operation, and since int type is not a subclass of bool that would never work anyway.

Python 3 behaves as expected:

>>> True.__lt__(2) True 

So, how is True < 2 implemented in Python 2?

Answer 1

True is equal to 1 in Python (which is why it's less than 2) and bool is a subclass of int: basically, False and True are 0 and 1 with funky repr()s.

As to how comparison is implemented on integers, Python uses __cmp__(), which is the old-school way of writing comparisons in Python. (Python 3 doesn't support __cmp__(), which is why it's implemented as __lt__() there.) See https://docs.python.org/2/reference/datamodel.html#object.__cmp__