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Python Program to Print the Fibonacci Series

Beginner · Numbers · CBSE class 11 practical list · CBSE class 12 practical list

The Fibonacci series starts with 0 and 1, and each next term is the sum of the two terms before it: 0, 1, 1, 2, 3, 5, 8, 13 and so on. This program prints the first n terms of the series.

Program

fibonacci_series.py
n = 10 # or: n = int(input("How many terms? "))
a = 0 # first term
b = 1 # second term
print("First", n, "terms of the Fibonacci series:")
for i in range(n):
print(a, end=" ")
next_term = a + b
a = b
b = next_term
print()
Output
First 10 terms of the Fibonacci series:
0 1 1 2 3 5 8 13 21 34

How it works

  1. a and b hold the two most recent terms, starting at 0 and 1.
  2. Each pass of the loop prints a, then works out the next term as a + b.
  3. The terms then move along by one: a takes the value of b, and b takes the new term.
  4. end=" " prints the terms on one line, and the final print() ends that line.

Other ways to write it

Using recursion

Using recursion
def fibonacci(k):
# Term k is the sum of terms k - 1 and k - 2
if k <= 1:
return k
return fibonacci(k - 1) + fibonacci(k - 2)
series = []
for i in range(10):
series.append(fibonacci(i))
print("Fibonacci series:", series)
Output
Fibonacci series: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

A recursive function matches the definition closely, but it repeats a lot of work and gets slow beyond about 30 terms.

Terms up to a limit

Terms up to a limit
limit = 100
a, b = 0, 1
series = []
while a <= limit:
series.append(a)
a, b = b, a + b
print(f"Fibonacci numbers up to {limit}: {series}")
Output
Fibonacci numbers up to 100: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

A while loop suits a limit on the value rather than a count of terms, and a, b = b, a + b updates both terms at once.

Try it yourself

Change the program to print only the even terms among the first 20.

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