Why is the result different ,despite the code is exactly the same?

Question

I want to build a function that sums two numpy arrays into a new array if and only if the distinct indices are euqal.

x = np.array([2,1,1,1])
y=np.array([2,1,0,1])   

overlap = np.zeros(4)
for i in range(0,len(x)):
    if x[i] == y[i]:
        overlap[i]= x[i]+y[i]

print(overlap)
[4. 2. 2. 2.]

That worked as expected. Now I want to define the function, but the ouput is different, despite that the code is exactly the same.

    def sum_overlap(x,y):
       overlap = np.zeros(4)
       for i in range(0,len(x),1):
           if x[i] == y[i]:
              overlap[i] = x[i] + y[i]
              print(overlap)

sum_overlap(x,y)
[4. 0. 0. 0.]
[4. 2. 0. 0.]
[4. 2. 2. 0.]
[4. 2. 2. 2.]

I think it has something to do with the iterator, but i cant figure it out.

Answer 1

Your print statement is in the loop, so everytime it gets called it prints out the list. Take the print statement out of the loop but remain in the function and your outputs should be the same

Answer 2

The working code:

def sum_overlap(x,y):
    overlap = np.zeros(4)
    for i in range(0,len(x),1):
        if x[i] == y[i]:
            overlap[i] = x[i] + y[i]
    return overlap