Print Fibonacci series in python

What is Fibonacci series?
A Fibonacci series is a sequence of numbers where each number is a sum of previous 2 numbers. First two terms of a Fibonacci series are 0 and 1.
This article will explain how to print Fibonacci series in python using for loop and recursion with example programs.

Method 1: Using for loop
This approach is based on the following algorithm
1. Declare two variables representing two terms of the series. Initialize them to 0 and 1 as the first and second terms of the series respectively.
2. Initialize another variable to 0. This will be the for loop counter.
3. Loop from 0 to the total number of terms in the series.
4. In every iteration,
A. add the variables defined in step 1. This represents a term(or item) of the Fibonacci series.
B. assign the value of second variable to first and the sum in above step A to the second variable.

Python program to generate Fibonacci series written as per the above algorithm follows.

# read the total number of items in Fibonacci series
max_item_input = input("Enter the number of items in Fibonacci series\n")
max_item = int(max_item_input)
# variables to hold two items of series
first = 0
second = 1
# loop counter
item = 0
# iterate till the total number of items in the series
for item in range(max_item):
    # add two terms, the result represents the subsequent element of the series
    sum = first + second
    # print current item
    print(first,end = ",")
    # assign variables
    first = second
    second = sum
    # increment loop counter
    item += 1

This program prints the following output

Method 2: Using recursion
A recursive function calls itself again and again till some condition is met.

Create a recursive function that receives an integer as argument. This integer argument represents the position in Fibonacci series and returns the value at that position. Thus, if it receives 5, it returns the value at 5th position in the Fibonacci series.

This recursive function returns 0 and 1 if the argument value is 0 or 1. For all other values, it calls itself with the sum of nth and (n-1)th positions.

The program reads the total number of elements in the Fibonacci series as input from keyboard. It then initiates a loop starting from 0 till the input value. In every iteration, the recursive function is called and the resultant Fibonacci item for that position is printed.

def fibonacci(number):
    # return 0 and 1 for first and second terms
    if number == 0:
        return 0
    elif number == 1:
        return 1
    else:
        # return the sum of two numbers
        return fibonacci(number - 1) + fibonacci(number - 2)

# read the total number of items in Fibonacci series
max_item_input = input("Enter the number of items in Fibonacci series\n")
max_item = int(max_item_input)

# iterate from 0 till number of terms
for count in range(max_item):
    print(fibonacci(count), end=",")

Output of above execution is

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