What Is Recursion?

What Is Recursion?
👉 Recursion is a type of program where you get a subroutine to call itself. It gets kinda hard to explain. I'd very much recommend this book, which does an excellent job of explaining this concept.
Recursion lets us solve problems in a more human way. Some mathematical problems can just be solved better using recursion.
For example:

We want to print out a sequence of the same emoji, reducing by 2 emojis per line. (eg print a row of 9, then a row of 7, then 5, etc. until we get none).

We will end up with a reverse pyramid pattern.
We could use range(), but it's a bit odd with counting backwards. Or a loop, but that would be pretty long.

👉 Here's an example of a recursive solution.

def reverse(value):
if value <= 0:
print("Done!")
return
# This `if` provides the 'stop' condition for the program. Otherwise it would run forever.

else: # if we're not at the stop condition.
for i in range(value):
print("💯", end="") # Outputs 'value' emojis
print() # New line
reverse(value - 2) # takes 2 off the value and calls the subroutine again with this new number. Eg if value was 7 it would call 'reverse(value)' again with value as 5.
reverse(5)

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