What is sys.maxint in Python 3?

Python 3 ints do not have a maximum.

If your purpose is to determine the maximum size of an int in C when compiled the same way Python was, you can use the struct module to find out:

>>> import struct
>>> platform_c_maxint = 2 ** (struct.Struct('i').size * 8 - 1) - 1

If you are curious about the internal implementation details of Python 3 int objects, Look at sys.int_info for bits per digit and digit size details. No normal program should care about these.

If you are looking for a number that is bigger than all others:

Method 1:

float('inf')

Method 2:

import sys
max = sys.maxsize

If you are looking for a number that is smaller than all others:

Method 1:

float('-inf')

Method 2:

import sys
min = -sys.maxsize - 1

Method 1 works in both Python2 and Python3. Method 2 works in Python3. I have not tried Method 2 in Python2.

The sys.maxint constant was removed, since there is no longer a limit to the value of integers. However, sys.maxsize can be used as an integer larger than any practical list or string index. It conforms to the implementation’s “natural” integer size and is typically the same as sys.maxint in previous releases on the same platform (assuming the same build options).

http://docs.python.org/3.1/whatsnew/3.0.html#integers

As pointed out by others, Python 3's int does not have a maximum size, but if you just need something that's guaranteed to be higher than any other int value, then you can use the float value for Infinity, which you can get with float("inf").

In Python 3.5 onwards, you can use math.inf.

Note: as per ely's comment, this may impact the efficiency of your code, so it may not be the best solution.