Prevent decorator from being used twice on the same function in python

Question

I have a decorator:

from functools import wraps
def d(f):
    @wraps(f)
    def wrapper(*args,**kwargs):
        print \'Calling func\'
        return f(*arg         


        

Answer 1

I'd store the information in the function itself. There is a risk of a conflict if multiple decorators decide to use the same variable, but if it's only your own code, you should be able to avoid it.

def d(f):
    if getattr(f, '_decorated_with_d', False):
        raise SomeException('Already decorated')
    @wraps(f)
    def wrapper(*args,**kwargs):
        print 'Calling func'
        return f(*args,**kwargs)
    wrapper._decorated_with_d = True
    return wrapper

Another option can be this:

def d(f):
    decorated_with = getattr(f, '_decorated_with', set())
    if d in decorated_with:
        raise SomeException('Already decorated')
    @wraps(f)
    def wrapper(*args,**kwargs):
        print 'Calling func'
        return f(*args,**kwargs)
    decorated_with.add(d)
    wrapper._decorated_with = decorated_with
    return wrapper

This assumes that you control all the decorators used. If there is a decorator that doesn't copy the _decorated_with attribute, you will not know what is it decorated with.