Python Max Function

问题:

How does the max function work when items in a list are not of the same type?

For example the following code returns [1,'3']

max([1,52,53],[1,'3']) => [1,'3']

回答1:

In Python2, the default comparison for objects of different types is to compare using the id of their types (obtained by casting the object pointers to integers). Here a link to the source: http://hg.python.org/cpython/file/2.7/Objects/object.c#l757

On my build, here is the ordering of types:

>>> sorted([bool, int, float, long, list, tuple, dict, str, unicode])
[<type 'bool'>, <type 'float'>, <type 'int'>, <type 'list'>, <type 'long'>,
 <type 'dict'>, <type 'str'>, <type 'tuple'>, <type 'unicode'>]

Numbers (except for complex) have compare methods that allow cross type comparison based on numeric value (i.e. a float can be compared with an int).

The None object is special. It compares less than everything else.

To see it all put together, use sorted to see the ordering:

>>> sorted(zoo)
[None, -5, -5.0, 0, 0.0, -0.0, False, True, 10, 10.0, 11.5, {},
 {'abc': 10}, {'lmno': 20}, [], [1, 2], [1, 2, 3], [1, [2, 3]],
 '', u'', 'alpha', u'alpha', 'bingo', 'cat', (), (1, 2), 
 (1, 2, 3), (1, (2, 3)), u'bingo', u'cat']

回答2:

In Python 2 objects of different types are compared by type's string representation using special logic. See Raymond's answer for details.

In Python 3 this code will raise an exception:

Traceback (most recent call last):
  File "prog.py", line 1, in <module>
    max([1,52,53],[1,'3'])
TypeError: unorderable types: str() > int()

回答3:

It does whatever the > operator does for the two elements.