cache-decorator.md

Python exercise: write a cache decorator

• Difficulty: medium
• Time to complete: 1-2h

Functional specs

Write a Python decorator that can be used to cache a function's result. Its API should look like this:

@cache(ttl=3600)
def slow_function():
    import time

    time.sleep(5)
    return "result"


assert slow_function() == "result"  # takes 5 seconds
assert slow_function() == "result"  # returns immediately

Technical specs

You are free to how to store results:

• In memory, with a simple dict
• On the file system
• In a Redis DB
• On AWS S3

To go further

Functional specs:

• Make sure this works as you would expect if the function accepts arguments

Developer experience:

• Add tests with pytest
• Add types with mypy
• Add linting with flake8
• Add autoformatting with black and isort