[Python] Explanation of Merge Sort for Dummies

I found this code online:

def merge(left, right):
result = []
i ,j = 0, 0
while i < len(left) and j < len(right):
if left <= right[j]:
result.append(left)
i += 1
else:
result.append(right[j])
j += 1
result += left[i:]
result += right[j:]
return result

def mergesort(list):
if len(list) < 2:
return list
middle = len(list) / 2
left = mergesort(list[:middle])
right = mergesort(list[middle:])
return merge(left, right)


It works 100% when I run it. I just do not really get how the merge sort works or how the recursive function is able to properly order both a left and a right.

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