Fibonacci sequence in python using generator

Question

def fibonacci_sequence():
    a,b = 1,1
    while True:
        yield a
        a,b = b, a+b

for i in range(10):
    print(fibonacci_sequence().__next__())

I tried using this in Python 3 to print out the fibonacci series. But the program just ends up printing 1 over and over again

Answer 1

You are declaring on each iteration a new generator you need to create one outside of the loop.

def fibonacci_sequence():
    a,b = 1,1
    while True:
        yield a
        a,b = b, a+b

generator = fibonacci_sequence()
for i in range(10):
    print(generator.__next__())

You could also use next()

generator = fibonacci_sequence()
for i in range(10):
    print(next(generator))

Answer 2

You are re-initializing the fibonacci_sequence each time in loop, do it like this:

def fibonacci_sequence():
    a,b = 1,1
    while True:
        yield a
        a,b = b, a+b

f = fibonacci_sequence()

for i in range(10):
    print(next(f))

Answer 3

As said already, you need to instantiate the generator once only, outside the loop.

Also, avoid calling __next__ directly, use next(generator/iterator) instead.

Having said that, in this simple case just let the for instruction handle the iteration protocol (ie call iter , call next and catch the StopIteration exception).

We can also write the loop as:

import itertools as it

def fibonacci_sequence():
    a,b = 1,1
    while True:
        yield a
        a,b = b, a+b

for k in it.islice(fibonacci_sequence(),10):
    print(k)