Simple Python Fibonacci Generator of Infinite Size Explained with Example

Before writing Python Fibonacci generator, you should know the Generator in Python and Fibonacci series

Prerequisite:

What is the Generator in Python?

In an earlier post, we have seen a Python generator.

As per the name “Generator”, is a function that generates the values (more than one or series of values).

What is Fibonacci Number Series?

It is a sequence of numbers in which every next term is the sum of the previous two terms.

However, this logic doesn’t apply to the first two terms of the sequence. The first two terms are initialized to 1.

The Fibonacci series looks like

1, 1, 2, 3, 5, 8, 13, 21, ...

Here is a simple Python program to print the Fibonacci series…

def fibonacci():
    a=0
    b=1
    for i in range(6):
        print(b)
        a,b= b,a+b

obj = fibonacci()

Output:

1
1
2
3
5
8

In a single function call, we are printing all the Fibonacci number series.

So, instead of using the function, we can write a Python generator so that every time we call the generator it should return the next number from the Fibonacci series.

Basically, we are using yield rather than return keyword in the Fibonacci function.

Python Fibonacci Generator

Here you go…

def fibonacciGenerator():
    a=0
    b=1
    for i in range(6):
        yield b
        a,b= b,a+b

obj = fibonacciGenerator()

print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))

Output:

1
1
2
3
5
8

If you look at the above program, you can see, the generator preserves the state. When you call next time, it executes from where it had terminated.

Python Fibonacci Generator of Infinite Size

Instead of using for loop we are using, while conditional loop in Python. When we pass True as an argument, while-condition always holds True.

def fibonacciGenerator():
    a=0
    b=1
    while(True):
        yield b
        a,b= b,a+b

obj = fibonacciGenerator()

print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))

print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))

print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj))

Output:

1
1
2
3
5
8
13
21
34
55
89
144
233
377
610
987
1597
2584

Now you can call fibonacciGenerator() function as many times you want. Every time you call it, it returns the next number from the Fibonacci series.

I have been asked to write a Python Fibonacci generator in many Python interview questions. Understand the concepts of how Generator works.

Any doubt? Write in the comment.