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up vote 17 down vote favorite
2

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?

share|improve this question
    
Via an implicit conversion to an integer maybe? – Carcigenicate yesterday
    
You might find this trick funny: [exprFalse, exprTrue][condition] is equivalent to exprTrue if condition else exprFalse – BlackBear 21 hours ago
3  
@BlackBear except that it evaluates both. print("True") if condition else print("False") vs [print("False"), print("True")][condition]. – immibis 21 hours ago
up vote 46 down vote

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, it 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__

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2  
Ah, yes that's it. I'd forgotten about ol' __cmp__. Thanks! – wim yesterday
3  
Be sure to mark kindall's post as correct if it helped you @wim – Andrew 10 hours ago
up vote 18 down vote

You didn't find super(bool, True).__lt__ because int uses the legacy __cmp__ method instead of rich comparisons on Python 2. It's int.__cmp__.

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up vote 2 down vote

True is a just name that refers to an object of type int, specifically value 1. Expression True < 2 is equal to 1 < 2. Same, False is equal to 0. In Python 2 you have a method __cmp__, that returns 0 if values are equals, -1 if is one value too greater than other value and 1 if is one value too less than other value. Example:

>>> True.__cmp__(1)
0
>>> True.__cmp__(0)
1
>>> True.__cmp__(-1)
1
>>> True.__cmp__(0)
1
>>> True.__cmp__(1)
0
>>> True.__cmp__(2)
-1

In Python 3 you have a __lt__ and __gt__ methods that are equivalents of < and >.

share|improve this answer
    
True is a just name that refers to an object of type int <-- I don't think that's right, the type of True is bool. A subclass of int. The subclass could, in principle, override the operation True < 2 to behave differently than 1 < 2. – wim 16 hours ago

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