Merging two ordered lists efficiently in Python

l1 = [1, 3, 5, 7, 9, 11]
l2 = [2, 4, 6]
p1 = 0
    p2 = 0
    result = []
    # Loop over both lists until one list is at the end
    while p1 < len(l1) and p2 < len(l2):
        # If the values at the positions are the same,
        # copy the value to the result
        if l1[p1] == l2[p2]:
            result.append(l1[p1])
            result[-1] = l1[p1] + l2[p2]
            p1 += 1
            p2 += 1
            # One entry is smaller, increment the smaller pointer
        elif l1[p1] < l2[p2]:
            result.append(l[p1])
            p1 += 1
        # One entry is smaller, increment the smaller pointer
        elif l1[p1] > l2[p2]:
            result.append(l2[p2])
            p2 += 1
    rest = []
    if p1 < len(l1):
        rest = l1[p1:len(l1)]
    elif p2 < len(l2):
        rest = list2[p2:len(l2)]
    result += rest
# [1, 2, 4, 5, 6, 7, 9, 11]