Add two lists of different lengths in python, start from the right

Question

I want to add two list of different length start from the right Here's an example

[3, 0, 2, 1]
[8, 7]

Expected result:

[3, 0, 10, 8]

These list represent coefficient of polynomials

Here is my implementation

class Polynomial:
    def __init__(self, coefficients):
        self.coeffs = coefficients

    def coeff(self, i):
        return self.coeffs[-(i+1)]

    def add(self, other):
        p1 = len(self.coeffs)
        p2 = len(other.coeffs)
        diff = abs(p1 - p2)
        if p1 > p2:
            newV = [sum(i) for i in zip(self.coeffs, [0]*diff+other.coeffs)]
        else:
            newV = [sum(i) for i in zip([0]*diff+self.coeffs, other.coeffs)]                  
        return Polynomial(newV)

    def __add__(self, other):
        return self.add(other).coeffs

This one work fine, just want to know anyway to do better, cleaner code? As python always stressed at clean code, I want to know is there any way to write cleaner, pythonic code?

Answer 1

Edit (2020-18-03):

>>> P = [3, 0, 2, 1]
>>> Q = [8, 7]
>>> from itertools import zip_longest
>>> [x+y for x,y in zip_longest(reversed(P), reversed(Q), fillvalue=0)][::-1]
[3, 0, 10, 8]

Obviously, if you choose a convention where the coefficients are ordered the opposite way, you can just use

P = [1, 2, 0, 3]
Q = [7, 8]
[x+y for x,y in zip_longest(P, Q, fillvalue=0)]

Answer 2

I believe a simple for loop is far simpler than a comprehension with zip_longest...

P = [3, 0, 2, 1]
Q = [8, 7]

A, B = sorted([P, Q], key=len)

for i, x in enumerate(reversed(A), 1):
   B[-i] += x

#print(B)

If you need to keep P unchanged, copy it first. Also, if Q is much smaller than P, this will be more effective.