sum of nested list in Python

Question

I try to sum a list of nested elements

e.g, numbers=[1,3,5,6,[7,8]] should produce sum=30

I wrote the following code :

Answer 1

One alternative solution with list comprehension:

>>> sum( sum(x) if isinstance(x, list) else x for x in L )
30

Edit: And for lists with more than two levels(thx @Volatility):

def nested_sum(L):
    return sum( nested_sum(x) if isinstance(x, list) else x for x in L )