Python Program to Print Fibonacci Series

You can print the Fibonacci series in Python using a loop with a, b = 0, 1 and repeatedly updating a, b = b, a + b inside a for loop to print the first n numbers.

Examples

Input5

Output0 1 1 2 3

Input1

Output0

Input0

Output

How to Think About It

To print the Fibonacci series, start with the first two numbers 0 and 1. Then, for each next number, add the previous two numbers together. Repeat this process until you have printed the desired count of numbers.

Algorithm

1

Get the number of terms to print from the user.

2

Initialize two variables with 0 and 1 for the first two Fibonacci numbers.

3

Use a loop to repeat for the number of terms.

4

Print the current number.

5

Update the two variables to the next two Fibonacci numbers by adding them.

6

End the loop after printing all terms.

Code

python

n = int(input('Enter number of terms: '))
a, b = 0, 1
for _ in range(n):
    print(a, end=' ')
    a, b = b, a + b

Output

Enter number of terms: 5
0 1 1 2 3 

Dry Run

Let's trace printing 5 Fibonacci numbers through the code

1

Input

n = 5

2

Initialize

a = 0, b = 1

3

Iteration 1

Print 0, update a=1, b=1

4

Iteration 2

Print 1, update a=1, b=2

5

Iteration 3

Print 1, update a=2, b=3

6

Iteration 4

Print 2, update a=3, b=5

7

Iteration 5

Print 3, update a=5, b=8

Iteration	a (current)	b (next)	Printed
1	0	1	0
2	1	1	1
3	1	2	1
4	2	3	2
5	3	5	3

Why This Works

Step 1: Start with first two numbers

We begin with a = 0 and b = 1 because the Fibonacci series starts with 0 and 1.

Step 2: Print current number

In each loop, we print the current number stored in a.

Step 3: Update numbers for next iteration

We update a, b = b, a + b to move forward in the series by setting a to the old b and b to the sum of old a and b.

Alternative Approaches

Using recursion

python

def fib(n):
    if n <= 1:
        return n
    return fib(n-1) + fib(n-2)

n = int(input('Enter number of terms: '))
for i in range(n):
    print(fib(i), end=' ')

Recursion is simple but inefficient for large n due to repeated calculations.

Using a list to store series

python

n = int(input('Enter number of terms: '))
fib_series = [0, 1]
for i in range(2, n):
    fib_series.append(fib_series[i-1] + fib_series[i-2])
print(*fib_series[:n])

Stores all numbers in a list, useful if you need to reuse the series later.

Complexity: O(n) time, O(1) space

Time Complexity

The loop runs n times, so the time complexity is O(n).

Space Complexity

Only a few variables are used, so space complexity is O(1).

Which Approach is Fastest?

The iterative approach is fastest and uses constant space, while recursion is slower and uses more memory.

Approach	Time	Space	Best For
Iterative loop	O(n)	O(1)	Printing series efficiently
Recursion	O(2^n)	O(n)	Simple code but inefficient
List storage	O(n)	O(n)	When series reuse is needed