How to fake/proxy a class in Python

Question

I wrote some wrapper which has another object as an attribute. This wrapper proxies (forwards) all attribute requests with __getattr__ and __setattr__

Answer 1

Generally, you can use the wrapt library (pypi), which does the heavy lifting for you:

The wrapt module focuses very much on correctness. It therefore goes way beyond existing mechanisms such as functools.wraps() to ensure that decorators preserve introspectability, signatures, type checking abilities etc. [...]

To ensure that the overhead is as minimal as possible, a C extension module is used for performance critical components

It supports creating custom wrapper classes. In order to add your own attributes, you need to declare them in such a way that wrapt doesn't try to pass them on to the wrapped instance. You can:

• Prefix the attribute with _self_ and add properties for access
• Declare the attribute at the class level, in addition to in __init__

• Use slots, if appropriate for your class (not mentioned in the docs), like this:

  class ExtendedMesh(ObjectProxy):
      __slots__ = ('foo')
  
      def __init__(self, subject):
          super().__init__(subject)
          self.foo = "bar"
  

It also supports function wrappers, which might suit your purpose.