Question

I often find myself doing inefficient loops as such:

def __add__(self, other):
    dimensions = []
    for i in range(max(self.numberOfDimensions, other.numberOfDimensions)):
        a = None    
        if i < self.numberOfDimensions:
            a = self[i]     
        b = None    
        if i < other.numberOfDimensions:
            b = other[i]    

        # Doesn't actually do the right thing here.
        dimensions.append(sum(map(lambda x: ((x is None) and 1 or 2) - 1, (a, b))))

    return self.__class__(dimensions)

The calculation is simple, it’s just handling the if statements types that’s getting me. By the way, this is a subclass of tuple in which the add operator adds similar index’s values like so (1, 2, 3) + (4, 5, 6, 7) == (5, 7, 9, 7). I would think that filter() would help me out on this but I’m not sure how I’d implement it.

EDIT: This is for Python 3.

Answer 1

The most concise way to do this is

map(sum, itertools.izip_longest(self, other, fillvalue=0))

or

itertools.starmap(operator.add, 
                  itertools.izip_longest(self, other, fillvalue=0))

This does what I guess your original code is supposed to do. If you are using Python 3, convert the result to a tuple or list or whatever you want it to be.