Python Program to Print the Fibonacci sequence

To understand this example, you should have knowledge of following Python programming topics:

Python if...elif...else and Nested if

Python while Loop

A Fibonacci sequence is the integer sequence of 0, 1, 1, 2, 3, 5, 8.... The first two terms are 0 and 1. All other terms are obtained by adding the preceding two terms. This means to say the nth term is the sum of (n-1)th and (n-2)th term.

Source Code

# Program to display the Fibonacci sequence up to n-th term where n is 

provided by the user

# take input from the user
nterms = int(input("How many terms? "))

# first two terms
n1 = 0
n2 = 1
count = 2

# check if the number of terms is valid
if nterms <= 0:
   print("Plese enter a positive integer")
elif nterms == 1:
   print("Fibonacci sequence:")
   print(n1)
else:
   print("Fibonacci sequence:")
   print(n1,",",n2,end=', ')
   while count < nterms:
       nth = n1 + n2
       print(nth,end=' , ')
       # update values
       n1 = n2
       n2 = nth
       count += 1

Output

How many terms? 10
Fibonacci sequence:
0, 1, 1, 2, 3, 5, 8, 13, 21, 34,

Here, we ask the user for the number of terms in the sequence. We initialize the first term to 0 and the second term to 1. If the number of terms is more than 2, we use a while loop to find the next term in the sequence by adding the preceding two terms. We then interchange the variables (update it) and continue on with the process.