Writing a simple memoization decorator in Python

I was generating some reports recently that involved accessing expensive object methods whose results were known to not change on subsequent calls; However, instead of using local variables, I sketched-out this quick memoization decorator to save method responses as variables on the object (using a leading '_' followed by the method-name as the variable name):

def cache_method_results(fn):
    def _view(self, *args, **kwargs):
        var_name = '_{n}'.format(n=fn.__name__)

        if var_name in self.__dict__:  # Return the copy we have
            return self.__dict__[var_name]

        else:  # Run the function and save its result
            self.__dict__[var_name] = fn(self, *args, **kwargs)
            return self.__dict__[var_name]

    return _view

You might use it like this:

class Foo(object):
    @cache_method_results
    def some_expensive_operation(self):
        ...calculate something big and unchanging...
        return results

f = Foo()
print(f.some_expensive_operation())  # This first call will run the calculation
...
print(f.some_expensive_operation())  # but this one will used the cached result instead

It's not rocket science, but these little tricks add to the fun of using Python.