Python class decorator arguments

Question

I\'m trying to pass optional arguments to my class decorator in python. Below the code I currently have:

class Cache(object):
    def __init__(self, function         


        

Answer 1

I've learned a lot from this question, thanks all. Isn't the answer just to put empty brackets on the first @Cache? Then you can move the function parameter to __call__.

class Cache(object):
    def __init__(self, max_hits=10, timeout=5):
        self.max_hits = max_hits
        self.timeout = timeout
        self.cache = {}

    def __call__(self, function, *args):
        # Here the code returning the correct thing.

@Cache()
def double(x):
    return x * 2

@Cache(max_hits=100, timeout=50)
def double(x):
    return x * 2

Although I think this approach is simpler and more concise:

def cache(max_hits=10, timeout=5):
    def caching_decorator(fn):
        def decorated_fn(*args ,**kwargs):
            # Here the code returning the correct thing.
        return decorated_fn
    return decorator

If you forget the parentheses when using the decorator, unfortunately you still don't get an error until runtime, as the outer decorator parameters are passed the function you're trying to decorate. Then at runtime the inner decorator complains:

TypeError: caching_decorator() takes exactly 1 argument (0 given).

However you can catch this, if you know your decorator's parameters are never going to be a callable:

def cache(max_hits=10, timeout=5):
    assert not callable(max_hits), "@cache passed a callable - did you forget to parenthesize?"
    def caching_decorator(fn):
        def decorated_fn(*args ,**kwargs):
            # Here the code returning the correct thing.
        return decorated_fn
    return decorator

If you now try:

@cache
def some_method()
    pass

You get an AssertionError on declaration.

On a total tangent, I came across this post looking for decorators that decorate classes, rather than classes that decorate. In case anyone else does too, this question is useful.