Create a wrapper class to call a pre and post function around existing functions?

Question

I want to create a class that wraps another class so that when a function is run through the wrapper class a pre and post function is run as well. I want the wrapper class t

Answer 1

You're almost there, you just need to do some introspection inside __getattr__, returning a new wrapped function when the original attribute is callable:

class Wrapper(object):
    def __init__(self,wrapped_class):
        self.wrapped_class = wrapped_class()

    def __getattr__(self,attr):
        orig_attr = self.wrapped_class.__getattribute__(attr)
        if callable(orig_attr):
            def hooked(*args, **kwargs):
                self.pre()
                result = orig_attr(*args, **kwargs)
                # prevent wrapped_class from becoming unwrapped
                if result == self.wrapped_class:
                    return self
                self.post()
                return result
            return hooked
        else:
            return orig_attr

    def pre(self):
        print ">> pre"

    def post(self):
        print "<< post"

Now with this code:

number = Wrapper(Simple)

print "\nCalling wrapped 'one':"
number.one()

print "\nCalling wrapped 'two':"
number.two("2")

The result is:

Calling wrapped 'one':
>> pre
one
<< post

Calling wrapped 'two':
>> pre
two2
<< post

Answer 2

I have just noticed in my original design there is no way of passing args and kwargs to the wrapped class, here is the answer updated to pass the inputs to the wrapped function...

class Wrapper(object):
def __init__(self,wrapped_class,*args,**kargs):
    self.wrapped_class = wrapped_class(*args,**kargs)

def __getattr__(self,attr):
    orig_attr = self.wrapped_class.__getattribute__(attr)
    if callable(orig_attr):
        def hooked(*args, **kwargs):
            self.pre()
            result = orig_attr(*args, **kwargs)
            self.post()
            return result
        return hooked
    else:
        return orig_attr

def pre(self):
    print ">> pre"

def post(self):
    print "<< post"