Summary - Advanced decorators

Combine lru_cache, partial and class decorator to write a cache layer.

Summary - Advanced decorators

This group covered advanced decorators. A parameterized decorator has three layers: factory → decorator → wrapper. A class decorator holds state through __call__.

The functools module gave us three tools: wraps preserves metadata, lru_cache caches results, partial binds arguments, and reduce folds a sequence into one value.

The final task combines a parameterized decorator with lru_cache: repeat count and caching side by side.

Exercise Combine repeat and lru_cache

Write the parameterized repeat(n) decorator (factory, deco, wrapper; with @wraps(fn)). wrapper calls fn(*args) n times and returns the last result. Decorate slow_square(n) with @lru_cache(maxsize=None) and @repeat(3) (lru_cache on top). Print the result of slow_square(4).

Show example solution

from functools import wraps, lru_cache

def repeat(n):
    def deco(fn):
        @wraps(fn)
        def wrapper(*args):
            result = None
            for _ in range(n):
                result = fn(*args)
            return result
        return wrapper
    return deco

@lru_cache(maxsize=None)
@repeat(3)
def slow_square(n):
    return n * n

print(slow_square(4))

Test yourself

In what order does the combined decorator chain run?
- lru_cache first, then repeat
- repeat first, then lru_cache
- In parallel at the same time
- Only repeat; lru_cache is ignored
Show answer

repeat first, then lru_cache — @repeat(3) is applied first; each call then caches the wrapped function's result via lru_cache.

Combine the decorator with lru_cache

from functools import wraps, lru_cache

@____(maxsize=None)
@repeat(3)
def slow_square(n):
    return n * n

Show answer

from functools import wraps, lru_cache

@lru_cache(maxsize=None)
@repeat(3)
def slow_square(n):
    return n * n

Match the group concepts

repeat(n)

Parameterized factory
class Counter

Holds state
lru_cache

Result cache
partial

Binds arguments

Next lesson: Basic hints

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