Allow multiple delegations to stack, as well as optional prefixes

README.md

@@ -32,3 +32,26 @@ except e:
 
 assert raised
 ```
+
+Delegation can also be called multiple times on the same class, and there is an
+optional `prefix` option which allows the attribute name to be prefixed on the
+delegating class:
+
+```python
+from delegate import delegate
+
+class Parent:
+    def __init__(self):
+        self.a = "a"
+        self.b = "b"
+
+@delegate("a", to="parent")
+@delegate("b", to="parent", prefix="_")
+class Child:
+    def __init__(self):
+        self.parent = Parent()
+        self.c = "c"
+
+instance.a
+instance._b
+```

delegate/__init__.py

@@ -1,18 +1,21 @@
 #!/usr/bin/env python3
 
-def bind(instance, func, name):
-    """Turn a function into a bound method on instance"""
-    setattr(instance, name, func.__get__(instance, instance.__class__))
-
 def delegate(*args, **named_args):
-    dest = named_args.get('to')
-    if dest is None:
+    _dest = named_args.get('to')
+    if _dest is None:
         raise ValueError(
             "the named argument 'to' is required on the delegate function")
+
+    _prefix = named_args.get('prefix', '')
+
+    print(_dest, _prefix)
+
     def wraps(cls, *wrapped_args, **wrapped_opts):
         """Wrap the target class up in something that modifies."""
         class Wrapped(cls):
 
+            _delegates = [(a, _dest, _prefix) for a in args] + getattr(cls, '_delegates', [])
+
             def __getattr__(self, name):
                 """
                 Return the selected name from the destination if the name is one
@@ -21,27 +24,34 @@ def __getattr__(self, name):
                 error when `name` is not one of the selected args to be
                 delegated.
                 """
-                if name in args: return getattr(self.__dict__[dest], name)
+                for attr, dest, prefix in self._delegates:
+                    if name == prefix + attr:
+                        return getattr(self.__dict__[dest], name[len(prefix):])
+
                 raise AttributeError(f"'{self.__class__.__name__}' has no attribute '{name}'")
 
             def __setattr__(self, name, value):
                 """
                 If this name is one of those selected, set it on the destination
                 property. Otherwise, set it on self.
                 """
-                if name in args: setattr(getattr(self, dest), name, value)
-                else: self.__dict__[name] = value
+                for attr, dest, prefix in self._delegates:
+                    if name == prefix + attr:
+                        setattr(getattr(self, dest), name[len(prefix):], value)
+                        return
+                self.__dict__[name] = value
 
             def __delattr__(self, name):
                 """Delete name from `dest` or `self`"""
-                if name in args: delattr(getattr(self, dest), name)
-                else: del self.__dict__[name]
+                for attr, dest, prefix in self._delegates:
+                    if name == prefix + attr:
+                        delattr(getattr(self, dest), name[len(prefix):])
+                        return
 
-            def __init__(self, *wrapped_args, **wrapped_opts):
-                super().__init__(*wrapped_args, **wrapped_opts)
+                del self.__dict__[name]
 
         Wrapped.__doc__ = cls.__doc__ or \
-            f"{cls.__class__} wrapped to delegate {args} to its {dest} property"
+            f"{cls.__class__} wrapped to delegate {args} to its {_dest} property"
         Wrapped.__repr__ = cls.__repr__
         Wrapped.__str__ = cls.__str__
         Wrapped.__name__ = cls.__name__

test-delegate.py

@@ -4,8 +4,10 @@ class Parent:
     def __init__(self):
         self.a = "a"
         self.b = "b"
+        self.d = "d"
 
 @delegate("a", "b", to="parent")
+@delegate("d", to="parent", prefix="_")
 class Child:
     """A class with a delegate"""
     def __init__(self):
@@ -41,5 +43,9 @@ def expect_raises(errtype):
 assert instance.__class__.__name__ == "Child"
 with expect_raises(AttributeError):
     instance.z
+with expect_raises(AttributeError):
+    instance.d
+instance._d
+assert len(Child._delegates) == 3
 
 print("TESTING delegate()...done")