Decorator classes in Python

Question

I want to construct classes for use as decorators with the following principles intact:

1. It should be possible to stack multiple such class decorators on top off 1 function.
2. The resulting function name pointer should be indistinguishable from the same function without a decorator, save maybe for just which type/class it is.
3. Ordering off the decorators should not be relevant unless actually mandated by the decorators. Ie. independent decorators could be applied in any order.

This is for a Django project, and the specific case I am working on now the method needs 2 decorators, and to appear as a normal python function:

@AccessCheck @AutoTemplate def view(request, item_id) {} 

@AutoTemplate changes the function so that instead of returning a HttpResponse, it just returns a dictionary for use in the context. A RequestContext is used, and the template name is inferred from the method name and module.

@AccessCheck adds additional checks on the user based on the item_id.

I am guessing it's just to get the constructor right and copy the appropriate attributes, but which attributes are these?

The following decorator won't work as I describe:

class NullDecl (object):     def __init__ (self, func):         self.func = func     def __call__ (self, * args):         return self.func (*args) 

As demonstrated by the following code:

@NullDecl @NullDecl def decorated():     pass  def pure():     pass  # results in set(['func_closure', 'func_dict', '__get__', 'func_name', # 'func_defaults', '__name__', 'func_code', 'func_doc', 'func_globals']) print set(dir(pure)) - set(dir(decorated)); 

Additionally, try and add "print func.name" in the NullDecl constructor, and it will work for the first decorator, but not the second - as name will be missing.

Refined eduffy's answer a bit, and it seems to work pretty well:

class NullDecl (object):     def __init__ (self, func):         self.func = func         for n in set(dir(func)) - set(dir(self)):             setattr(self, n, getattr(func, n))      def __call__ (self, * args):         return self.func (*args)     def __repr__(self):         return self.func 

Answer 1

A do-nothing decorator class would look like this:

class NullDecl (object):    def __init__ (self, func):       self.func = func       for name in set(dir(func)) - set(dir(self)):         setattr(self, name, getattr(func, name))     def __call__ (self, *args):       return self.func (*args) 

And then you can apply it normally:

@NullDecl def myFunc (x,y,z):    return (x+y)/z