Python error explained
RecursionError: what it means and how to fix it
A function kept calling itself and never stopped.
The message
RecursionError: maximum recursion depth exceededWhat it means
A recursive function calls itself on a smaller problem until it reaches a base case that returns without recursing. Without a base case, or if the problem never gets smaller, it would go on for ever, so Python stops it after about 1,000 calls.
Common causes
- A missing base case
- A base case that is never reached, like checking n == 0 when n goes negative
- Calling the function with the same argument instead of a smaller one
Example that raises it
def countdown(n):
print(n)
countdown(n - 1)
countdown(3)
The fix
def countdown(n):
if n == 0:
print("Lift off!")
return
print(n)
countdown(n - 1)
countdown(3)
Tip: Write the base case first. Make sure every recursive call moves closer to it.
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