Return two python lists?
I'm not sure how the return in the following comparison function works? Why can he return this format?
def func(self, num):
num = sorted([str(x) for x in num], cmp=self.compare)
def compare(self, a, b):
return [1, -1][a + b > b + a]
+3
umassjin
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2 answers
It doesn't return two lists. It returns one of two values from the first list. Consider this rewriting:
def compare(self, a, b):
possible_results = [1, -1]
return possible_results[a + b > b + a]
It takes advantage of the fact that True
in Python it treats a value 1
, but False
treats it as a value 0
and uses them as indexes of a list.
+6
Amber
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Boolean False is zero, and Boolean True is one. They can be used as indices on a list:
# Normal indexing with integers
>>> ['guido', 'barry'][0]
'guido'
>>> ['guido', 'barry'][1]
'barry'
# Indexing with booleans
>>> ['guido', 'barry'][False]
'guido'
>>> ['guido', 'barry'][True]
'barry'
# Indexing with the boolean result of a test
>>> ['guido', 'barry'][5 > 10]
'guido'
>>> ['guido', 'barry'][5 < 10]
'barry'
Hope everything is clear :-)
+3
Raymond Hettinger
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