import itertools
A = [50, 60, 70]
B = [0.3, 0.1, 0.5, 0.4]
print [a + b for a, b in itertools.product(A, B)]
>> [50.3,50.1,50.5,50.4,60.3,60.1,60.5,60.4,70.3,70.1,70.5,70.4]
In the above code, is there a way to just return the minimum value of a + b for each a? so the output should be:
[50.1,60.1,70.1]
please note this is a toy example, in the real example A and B are lists of lat and lon values and I compute the great circle distance between them
itertools.product isn't really appropriate for your Great Circle task because it lumps all the (A, B) pairs into one container, but you want to keep all the pairs with a given A value together in a sub-container so you can find their minimum. So just use a pair of nested loops. If you want, you can do it as a generator expression to calculate the minimum value nested inside a list comprehension, like this:
A = [50, 60, 70]
B = [0.3, 0.1, 0.5, 0.4]
f = lambda x, y: x + y
print [min(f(a,b) for b in B) for a in A]