Python also accepts function recursion, which means a defined function can call itself.

Recursion is a common mathematical and programming concept. It means that a function calls itself. This has the benefit of meaning that you can loop through data to reach a result.

The developer should be very careful with recursion as it can be quite easy to slip into writing a function which never terminates, or one that uses excess amounts of memory or processor power. However, when written correctly recursion can be a very efficient and mathematically$-$elegant approach to programming.

In this example, tri$\_$recursion$()$ is a function that we have defined to call itself $("$recurse$").$ We use the k variable as the data, which decrements $(-1)$ every time we recurse. The recursion ends when the condition is not greater than $0($i$.$e$.$ when it is $0).$

To a new developer it can take some time to work out how exactly this works, best way to find out is by testing and modifying it$.$

Try the Recursion Example and report how many times the tri$\_$recursion$()$ is called.

def tri$\_$recursion$($k$)$:

$$if$($k$>0)$:

$$ result $=$ k$+$tri$\_$recursion$($k$-1)$

$$ print$($result$)$

$$else:

$$ result $=0$

$$return$$result

print$("$

Recursion Example Results"$)$

tri$\_$recursion$(6)$

Try the Recursion Example and report how many times the tri$\_$recursion$()$ is called.

$```$

def tri$\_$recursion$($k$)$:

if$($k$>0)$:

result $=$ k$+$tri$\_$recursion$($k$-1)$

print$($result$)$

else:

result $=0$

return result

$```$

print$("$

Recursion Example Results"$)$

tri$\_$recursion$(6)$