"I forgot to implement that method."
This sentence has caused production bugs.
Python's ABCs (Abstract Base Classes) prevent this.
Now any storage backend must implement these methods.
Forget one? Python tells you at instantiation, so you'll catch it in time:
class InMemoryRepo(SnippetRepository):
def add(self, snippet):
...
# Forgot list()? → TypeError immediately
This is a *contract*: your code can't lie about what it supports.
Tomorrow's free LIVE session covers how to structure real Python projects using these patterns.
Bob Belderbos