Python | Recursive Function

Python - Recursive Function

Recursive function means the function call themselves within the function body until a certain condition is matched then this function is recursive function.

For example:- 

def fact(n):

     if n==0 or n==1:

          return 1

     else:

          return n*fact(n-1)

print(fact(8))

Output:-

40320

This is the example of recursive function. In this program we create a function named as fact and we call this function within the same function.

How this program works?

We give the value of n is 8 so n=8. In the first if condition, 8 is not equal to 0 and 1 so it goes to the else part in the else part the sentence is return n*fact(n-1) that means 8*fact(7) now here value of n become 7 to find fact(7) again same procedure repeat up to fact(1).  Because fact(1)=1  we give this condition. Then 

fact(2) => 2*fact(1) => 2*1=> 2  

fact(3)=> 3*fact(2) => 3*2=> 6

fact(4)=>4*fact(3)=>4*6=>24

fact(5)=>5*fact(4)=>5*24=>120

fact(6)=>6*fact(6)=>6*120=>720

fact(7)=>7*fact(6)=>7*720=>5040

fact(8)=>8*fact(7)=>8*5040=>40320

All this process done in background to find factorial using recursive. You can write this program without using recursive function. Now we will see how to write this program without using recursive function.

num = 8

fact = 1

if num == 0 or num == 1:

     print("1")

else:

     for i in range(1,num+1):

          fact = fact*i

     print(fact)

     

Output:

40320

You can see the difference of both programs. Recursive function reduce unnecessary functions. Recursive function reduce the size of program. In recursive function you must have to write if condition because they call themselves until certain condition is matched. 

We will see another example of recursive function.

1) Fibonacci series 

Ans:-

def fib(n):

     if n == 0:

          return 0

     elif n == 1:

          return 1

     else:

          return fib(n-1)+fib(n-2)

for i in range(10):

     print(fib(i))

     

Output:

0

1

1

2

3

5

8

13

21

34

There are some disadvantages of recursive function. Sometimes logic behind the recursive function is hard. Recursive function takes lot of memory and time to run. Recursive function are hard to debug. 

In the next section we will see Built in function in python. 

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