Jason Swails於 2013年3月28日星期四UTC+8上午4時33分08秒寫道： > On Wed, Mar 27, 2013 at 3:49 PM, Joseph L. Casale <jca...@activenetwerx.com> > wrote: > > I have a class which sets up some class vars, then several methods that are > passed in data > > and do work referencing the class vars. > > > > > > I want to decorate these methods, the decorator needs access to the class > vars, so I thought > > about making the decorator its own class and allowing it to accept args. > > > > > > I was hoping to do all the work on in_data from within the decorator, which > requires access > > to several MyClass vars. Not clear on the syntax/usage with this approach > here, any guidance > > would be greatly appreciated! > > > > My guess is that you don't quite 'get' decorators yet (since I remember > similar types of questions when trying to learn them myself). Decorators > execute when the class type itself is being built (e.g., when a module is > first imported at runtime). So decorators will never take instance variables > as arguments (nor should they, since no instance can possibly exist when they > execute). Bear in mind, a decorator should take a callable as an argument > (and any number of 'static' parameters you want to assign it), and return > another callable. > > > > I provide an example decorator using the format the I typically adopt below > (where the decorator is a simple function, not a class): > > > def my_decorator(fcn):
I might add default parameters here if I am programming in python to save the troubles of subclassing similar decorators. But that is only the stylish problem in python. I might need to translate the decorator part into cython or c/c++ in the future. > """ Decorator for a function """ > > def new_fcn(self, *args, **kwargs): > """ This is the new function that we will return. """ > # You can access any instance variables here > returnval = fcn(self, *args, **kwargs) > > # Do anything else here with instance variables > return returnval # or any other return value you want > > return new_fcn > > > Notice here I define a new_fcn callable function that takes self and an > arbitrary argument/keyword-argument list, and I return this function (which > does not get called) to replace the function I passed in. You can use > instance variables inside new_fcn since new_fcn is called by instances of > MyClass. This is a very simple type of decorator, but hopefully helps > illustrate what decorators are. There is a particularly good thread on SO > with information about decorators here: > http://stackoverflow.com/questions/739654/understanding-python-decorators > > > > Hope this helps, > Jason -- http://mail.python.org/mailman/listinfo/python-list
