Sum a list which contains 'None' using Python

Question

Basically my question is say you have an list containing 'None' how would you try retrieving the sum of the list. Below is an example I tried which doesn't work and I get the error: TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'. Thanks

def sumImport(self):     my_list = [[1,2,3,None],[1,2,3],[1,1],[1,1,2,2]]     k = sum(chain.from_iterable(my_list))     return k 

Answer 1

You can use filter function

>>> sum(filter(None, [1,2,3,None])) 6 

Updated from comments

Typically filter usage is filter(func, iterable), but passing None as first argument is a special case, described in Python docs. Quoting:

If function is None, the identity function is assumed, that is, all elements of iterable that are false are removed.