This tutorial will discuss what recursive functions are and how to create and why we need them in python. So let's discuss Python Recursion.

## Python Recursion

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What are recursive functions?
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Until now, we were defining a function, and we were calling it from outside the function at the time of execution. What if we call the function inside the function? It will create a kind of loop of what recursion functions are all about. A recursive function is a function that can call itself during execution. For example, when a function body has a statement in which it calls itself, that function will be termed a recursive function. We have said that recursion acts like loops that can perform repetitive work, so there should be a base condition that stops that repetitive statement and give a result. You will get trapped in the infinite loop.

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Python Recursive Function
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There are many examples in which a function calls another function, but those are not recursive functions only those functions are recursive functions that can call themselves. Finding the factorial of a number is one of the classic examples of recursive functions. If you do not know what a factorial is, let’s understand it first. Factorial is a Math concept denoted by an exclamation mark (!). If you want the factorial of 5, you will write 5! And the solution of the factorial would be 5!= 5 x 4 x 3 x 2 x 1 = 120 And for note 1! =1 and 0! =1
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Let’s code the factorial in python
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def fact(n): if n==1 or n==0: #Base condition return 1 else: return n * fact(n-1) # recursion function calling num=7 print("the factorial of" ,num, "is ", fact(num)) #function calling

#Output

the factorial of 7 is 5040

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Behind the code:
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In the above example, to execute the function
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fact
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(), we call it from outside the function, then the value of variable
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num
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gets assigned to the function argument
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n,
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and the function gets started to execute when the argument
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n
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does not satisfy the
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if
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statement the
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else
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statement gets executed. In the
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else
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statement, we strike the recursive function, and let’s see how it works.

fact(n) #main function return 7 * fact(6) #recursive function first call return 7 * 6 *fact(5) #recursive function 2^{nd}call (the value of fact(6) is 6 * fact(5)) return 7*6*5*fact(4) #recursive function 3^{rd}call return 7*6*5*4 *fact(3) #recursive function 4^{th}call return 7*6*5*4*3*fact(2) #recursive function 5^{th}call return 7*6*5*4*3*2*fact(1) #recursive function 6^{th}call return 7*6*5*4*3*2*1 #recursive function 7^{th}call

At last, it returns a value of 7*6*5*4*3*2*1, and we get an output of 5040. Here you can see that the base condition plays a significant role what if we did not pass the base condition, the number kept on decreasing, and it could make an infinite recursive call.

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Pro and Cons of recursive function:
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Advantages:
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- With the recursion function, the code looks neat
- It divides the functionality into smaller parts which make the program easy to understand
- It comes very usefully with the binary trees data structure

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Disadvantages:
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- It isn’t easy to understand the logic behind every recursive function.
- A recursive function is slow as compared to the iterators.
- It occupies a lot of memory because we are executing the same function again and again
- it is very hard to debug the recursive function.
- With a big set of data, recursive functions are not useful