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Python Storing new value to array


New Coder

I am new to Python and I saw this two sum algorithm solution

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        prevMap = {}
        for i, n in enumerate(nums):
            diff = target - n
            if diff in prevMap:
                return [prevMap[diff], i]
            prevMap[i] = n

In this line prevMap[inedx] = n I should add a value at index but it return empty array [] or should I call it map or list ? but if I use it like this prevMap[n] = i it work correctly I don understant why ? I am comming from other languages where I store new value into array like this myarray[index] = value; so python is do it in the opposit way ?