Sum a list which contains 'None' using Python

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

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.

Remove None (and zero) elements before summing by using filter:

>>> k = sum(filter(None, chain.from_iterable(my_list)))
>>> k
20

To see why this works, see the documentation for filter:

filter(function, iterable)

Construct a list from those elements of iterable for which function returns true. iterable may be either a sequence, a container which supports iteration, or an iterator. If iterable is a string or a tuple, the result also has that type; otherwise it is always a list. If function is None, the identity function is assumed, that is, all elements of iterable that are false are removed.

Note that filter(function, iterable) is equivalent to [item for item in iterable if function(item)] if function is not None and [item for item in iterable if item] if function is None.