在包含字符串和整数的列表上使用max（）

Question

When I try to call the max() function on a list which contains a combination of integers and strings, it always returns a string, in Python 2.x

For example,

#input
li = [2, 232322, 78, 'python', 77]
max(li)

#output
'python'

What seems to be the logic behind this? How does Python compare a string with an integer?

Answer 1

In python2, strings and numbers compare in arbitrary but consistent order.

See Comparisons

Objects of different types, except different numeric types and different string types, never compare equal; such objects are ordered consistently but arbitrarily (so that sorting a heterogeneous array yields a consistent result

In python3, this raises a type error.

TypeError: unorderable types: str() > int()

Answer 2

The comparision between strings and numbers is undefined. It depends on the version of python. Strings are either always larger than any number or lower.

The manual states, that in CPython different objects are compared after their type name, if no other comparision is defined.

Answer 3

In Python 2.x The max() and min() functions first internally sort the list, resulting in a list similar to the output of list.sort() and then outputs the last (max) and first(min) item of the list-

>>> li = [2, 232322, 78, 'python', 77]
>>> max(li)
'python'
>>> min(li)
2

As you can see below if you sort the list the first and last item in the list are the result produce by min and max functions

>>> li = [2, 232322, 78, 'python', 77]
>>> li.sort()
>>> print li
[2, 77, 78, 232322, 'python']