[Solved] Return summation of two lists as elements in a new list

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I got requested result with below codes, another approach than what Marcos provided and I was able to find as well. Only additional thing is you need is to pad arrays to maximum length + 1 with numpy pad. 

def elementsum2array(arr1, arr2):

    '''
    1. Make the arrays of same length padding at the beginning/left side with 0's
    so that arrays get the same same length of "maximum length + 1" (for carry at the end).
    2. Get a new array of  length "maximum length + 1".
    3. Sum the elements of the arrays from last index to first index together with carry.
    4. Fill the new array element with sum % 10.
    5. Update carry (sum // 10).
    '''

    if len(arr1) == 0 and len(arr2) > 0:
        return arr2
    if len(arr1) > 0 and len(arr2) == 0:
        return arr1
    if len(arr1) == 0 and len(arr2) == 0:
        return []
    else:
        import numpy as np
        maxlen = max(len(arr1), len(arr2))
        arr1dif = maxlen - len(arr1) + 1
        arr2dif = maxlen - len(arr2) + 1
        arr1resized = np.pad(arr1, (arr1dif, 0), 'constant')
        arr2resized = np.pad(arr2, (arr2dif, 0), 'constant')
        L  = len(arr1resized)
        arrnew = [0 for num in range(maxlen+1)]
        carry = 0
        elementsum = 0

        for i in range(L-1, -1, -1):
            elementsum = (arr1resized[i] + arr2resized[i] + carry)
            arrnew[i] = elementsum % 10
            #print(arrnew[i])
            carry = elementsum // 10
            #print(carry)
            i=i-1

    return arrnew

Example:

arr1 = [3,2,1,0,4,9]
arr2 =     [5,1,6,4]
elementsum2array(arr1, arr2)
[0, 3, 2, 6, 2, 1, 3]

This was also done in Java here:
sum of two arrays element wise?

solved Return summation of two lists as elements in a new list