Why is int(50)<str(5) in python 2.x?

Question

In python 3, int(50)<'2' causes a TypeError, and well it should. In python 2.x, however, int(50)<'2' returns True (this is also the case for other number formats, but int exists in both py2 and py3). My question, then, has several parts:

1. Why does Python 2.x (< 3?) allow this behavior?

• (And who thought it was a good idea to allow this to begin with???)

What does it mean that an int is less than a str?

• Is it referring to ord / chr?
• Is there some binary format which is less obvious?

Is there a difference between '5' and u'5' in this regard?

Answer 1

It works like this¹.

>>> float() == long() == int() < dict() < list() < str() < tuple()
True

Numbers compare as less than containers. Numeric types are converted to a common type and compared based on their numeric value. Containers are compared by the alphabetic value of their names.²

From the docs:

CPython implementation detail: Objects of different types except numbers are ordered by >their type names; objects of the same types that don’t support proper comparison are >ordered by their address.

Objects of different builtin types compare alphabetically by the name of their type int starts with an 'i' and str starts with an s so any int is less than any str..

1. I have no idea.
   • A drunken master.
2. It means that a formal order has been introduced on the builtin types.
   • It's referring to an arbitrary order.
   • No.
3. No. strings and unicode objects are considered the same for this purpose. Try it out.

In response to the comment about long < int

>>> int < long
True

You probably meant values of those types though, in which case the numeric comparison applies.

^{1 This is all on Python 2.6.5}

^{2 Thank to kRON for clearing this up for me. I'd never thought to compare a number to a dict before and comparison of numbers is one of those things that's so obvious that it's easy to overlook.}

Answer 2

The reason why these comparisons are allowed, is sorting. Python 2.x can sort lists containing mixed types, including strings and integers -- integers always appear first. Python 3.x does not allow this, for the exact reasons you pointed out.

Python 2.x:

>>> sorted([1, '1'])
[1, '1']
>>> sorted([1, '1', 2, '2'])
[1, 2, '1', '2']

Python 3.x:

>>> sorted([1, '1'])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unorderable types: str() < int()