Question

Please i'm finding it difficult to grasp how recursion is being implemented in python. Can anyone walk me through on Recursion function. Maybe with a simple example. Thanks

Answer 1

A function with recursion is simply a function calling it self one or several times.

Here's a classic example using recursion to calculate the nth factorial:

def factorial(n):
if n == 0:
return 1
else:
return n * factorial(n - 1)

Answer 2

Ok i got this. so whats the difference between the recursion function and the while loop?

Answer 3

Like I wrote, a recursive function is a functiong calling it self. They usually have some condition to fill for the recursion to stop (n==0 in the case with the factorial function) and some value it modifies and passes as argument to reach that condition (factorial(n - 1) in the factorial case).

A while loop is a statement you (usually) find INSIDE a function and is used to repeat some pice of code untill a certain condition is meet.

Example python while loop:

print "1-9"

count = 1
while (count <= 9):
print 'count: ', count
count = count + 1

Answer 4

A recursive function solves part of a problem on each recursion. A recursive function has to satisfy three things: how to recurse more, when to stop recursing (this is called the base case) and what to do as it "unwinds" (all those recursions returning).

Reversing a string is a simple recursive task:

def reverse( string ):
if( len( string ) == 0 ):
# the base case
return ""
else:
char = string[ 0 ]
# recurse more, and on the unwind
# concatenate the string
return( reverse( string[ 1: ] ) + char )

if( __name__ == "__main__" ):
print reverse( "Hello World" )

Answer 5

I typically use factorials as a quick example of a problem to be solved recursively. A factorial of a number is the product of all integers less than or equal to that number. For example, 3! would be equal to 3x2x1=6, and 4! would be 4x3x2x1=24 etc. All you're really looking for in the answer is the factorial, but you have to do the same operation n number of times to actually arrive at that result. You could definitely do it with a loop, but a recursive solution is usually a bit more elegant based on code length.