def minimizeMaximumPair(lst):
lst.sort()
def compute(aList):
if len(aList) != 0:
return [(aList[0], lst[len(aList) - 1])].extend(compute(aList[1:len(aList) - 1]))
return []
return compute(lst)
When I get the the last recursion step I get an
TypeError: 'NoneType' object is not iterable
I tried returning nothing, and a []
The issue is when you call .extend().
Your compute function tries to return the value of .extend(), which is None. Similar to .sort(), .extend() modifies the object itself, rather than returning a modified copy of the object. This is known as mutability. Here's some working code:
def compute(aList):
if len(aList) != 0:
out = [(aList[0], lst[len(aList) - 1])]
out.extend(compute(aList[1:len(aList) - 1]))
return out
return []
Instead of list.extend which returns None, you can use list.__iadd__
__iadd__ also extends the list inplace, but returns the list afterward
if you have an aversion to using special methods, you can use iadd from the operator module
from operator import iadd
...
def compute(aList):
if len(aList) != 0:
return iadd([(aList[0], aList[-1])], compute(aList[1: -1]))
return []
aList[1: -1]. If you need more performance, you should look at passing extra parameters for the first and last index instead of actually slicing up the list.That's because extend is a function that doesn't return anything, it simply changes the list in-place. A possible solution is to use + instead:
return [(aList[0], lst[len(aList) - 1])] + compute(aList[1:len(aList) - 1])
