[SOLVED] Sorting a mixed list of ints and strings

Sorting a mixed list of ints and strings

I am trying to sort the following mixed list of ints and strings, but getting a TypeError instead. My desired output order is sorted integers then sorted strings.

x=[4,6,9,'ashley','drooks','chay','poo','may']
>>> x.sort()
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    x.sort()
TypeError: '<' not supported between instances of 'str' and 'int'

Solution

You can pass a custom key function to list.sort:

x = [4,6,9,'ashley','drooks','chay','poo','may']
x.sort(key=lambda v: (isinstance(v, str), v))

# result:
# [4, 6, 9, 'ashley', 'chay', 'drooks', 'may', 'poo']

This key function maps each element in the list to a tuple in which the first value is a boolean (True for strings and False for numbers) and the second value is the element itself, like this:

>>> [(isinstance(v, str), v) for v in x]
[(False, 4), (False, 6), (False, 9), (True, 'ashley'), (True, 'chay'),
 (True, 'drooks'), (True, 'may'), (True, 'poo')]

These tuples are then used to sort the list. Because False < True, this makes it so that integers are sorted before strings. Elements with the same boolean value are then sorted by the 2nd value in the tuple.