How to use a custom comparison function in Python 3?
Instead of a customsort(), you need a function that translates each word into something that Python already knows how to sort. For example, you could translate each word into a list of numbers where each number represents where each letter occurs in your alphabet. Something like this:
my_alphabet = ['a', 'b', 'c']
def custom_key(word):
numbers = []
for letter in word:
numbers.append(my_alphabet.index(letter))
return numbers
x=['cbaba', 'ababa', 'bbaa']
x.sort(key=custom_key)
Since your language includes multi-character letters, your custom_key function will obviously need to be more complicated. That should give you the general idea though.
Use the key
keyword and functools.cmp_to_key to transform your comparison function:
sorted(x, key=functools.cmp_to_key(customsort))
A complete python3 cmp_to_key lambda example:
from functools import cmp_to_key
nums = [28, 50, 17, 12, 121]
nums.sort(key=cmp_to_key(lambda x, y: 1 if str(x)+str(y) < str(y)+str(x) else -1))
compare to common object sorting:
class NumStr:
def __init__(self, v):
self.v = v
def __lt__(self, other):
return self.v + other.v < other.v + self.v
A = [NumStr("12"), NumStr("121")]
A.sort()
print(A[0].v, A[1].v)
A = [obj.v for obj in A]
print(A)
Use the key
argument (and follow the recipe on how to convert your old cmp
function to a key
function).
functools
has a function cmp_to_key
mentioned at docs.python.org/3.6/library/functools.html#functools.cmp_to_key