I am getting the wrong answer, and not sure why

[deanhystad]

This is a fun problem.

Triangles has a list N which it yields. A new N is generated each time triangles is called. HOWEVER, before the new N is generated you insert and append 0 to the old N.

This code prints the desired output because it prints the result of triangles() before they get "corrupted".

def triangles():
    N = [1]
    while True:
        yield N
        N.insert(0,0)
        N.append(0)
        N = [N[i]+N[i+1] for i in range(len(N)-1)]
 
for i, t in enumerate(triangles()):
    print(t)
    if i >= 5:
        break

An easy fix to your problem is to create to create a new N at the start of each iteration so you don't mess up the previous.

def triangles():
    N = [1]
    while True:
        yield N
        N = (0, *N, 0)
        N = [N[i]+N[i+1] for i in range(len(N)-1)]

# Or this one that uses zip and temporary lists.
def triangles():
    N = [1]
    while True:
        yield N
        N = [p + n for p, n in zip([0]+N, N+[0])]