## Key Concepts

Review core concepts you need to learn to master this subject

### Stack Overflow Error in Recursive Function

``````def myfunction(n):
if n == 0:
return n
else:
return myfunction(n-1)

myfunction(1000)  #results in stack overflow error``````

A recursive function that is called with an input that requires too many iterations will cause the call stack to get too large, resulting in a stack overflow error. In these cases, it is more appropriate to use an iterative solution. A recursive solution is only suited for a problem that does not exceed a certain number of recursive calls.

For example, `myfunction()` below throws a stack overflow error when an input of 1000 is used.

Recursion: Python
Lesson 1 of 2
1. 1
The best way to understand recursion is with lots of practice! At first, this method of solving a problem can seem unfamiliar but by the end of this lesson, we’ll have implemented a variety of algo…
2. 2
In the previous exercise, we used an iterative function to implement how a call stack accumulates execution contexts during recursive function calls. We’ll now address the conclusion of this funct…
3. 3
Now that we’ve built a mental model for how recursion is handled by Python, let’s implement the same function and make it truly recursive. To recap: We want a function that takes an integer as an …
4. 4
Excellent job writing your first recursive function. Our next task may seem familiar so there won’t be as much guidance. We’d like a function factorial that, given a positive integer as input, re…
5. 5
The previous exercise ended with a stack overflow, which is a reminder that recursion has costs that iteration doesn’t. We saw in the first exercise that **every recursive call spends time on th…
6. 6
Let’s use recursion to solve another problem involving lists: flatten(). We want to write a function that removes nested lists within a list but keeps the values contained. nested_planets = […
7. 7
So far our recursive functions have all included a single recursive call within the function definition. Let’s explore a problem which pushes us to use multiple recursive calls within the fun…
8. 8
Data structures can also be recursive. Trees are a recursive data structure because their definition is self-referential. A tree is a data structure which contains a piece of data **and reference…

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