Luhn algorithm in python

gistfile1.py

def validate(n):
    def process_1(index, nb, odd):
        result = (nb * 2 if index % 2 else nb) if odd else (nb * 2 if 0 == index % 2 else nb)
        return result - 9 if result > 9 else result
    n = [int(i) for i in str(n)]
    if len(n) % 2:
        n = [process_1(index, nb, True) for index, nb in enumerate(n)]
    else:
        n = [process_1(index, nb, False) for index, nb in enumerate(n)]
    return sum(n) % 10 == 0