[Python] Python sort lib different behavior with different comparing functions, some comparing...

For the comparing function function

from functools import cmp_to_key
def compare(a,b):
print(a,b, a+b,b+a,a+b>b+a)
return (a+b)>(b+a) # first comparing function

def sortArr(ls):
ls = sorted(ls,key =cmp_to_key(compare),reverse=True)
return "".join(ls)

ls = ["8","81","82","829"]
print(sortArr(ls))


Which will output as:

82 829 82829 82982 False
81 82 8182 8281 False
8 81 881 818 True
88182829


But using comparing function as:

from functools import cmp_to_key
def compare(a,b):
print(a,b, a+b,b+a,a+b>b+a)
return int(a+b) -int(b+a) # second comparing function

def sortArr(ls):
ls = sorted(ls,key =cmp_to_key(compare),reverse=True)
return "".join(ls)

ls = ["8","81","82","829"]
print(sortArr(ls))


the output is

82 829 82829 82982 False
81 82 8182 8281 False
8 81 881 818 True
8 82 882 828 True
8 829 8829 8298 True
88298281


Apparently the second sort function is what's needed. the first function didn't do all comparing use first element.

So why the first comparing function didn't work?

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