use descriptor/inheritance instead

Author: a2435191

paam/__init__.py

@@ -1,68 +1,79 @@
 from typing import Any, Callable, List
 from abc import ABC
 
-__all__ = ['GET', 'SET', 'DEL', 'Getter', 'Setter', 'Deleter', 'property_access_mod_class']
-
-class _PropertyAccessModifierBase(ABC):
+class _PaamBaseDescriptor(ABC):
     def __init__(self, obj: Any) -> None:
         self.is_setter  = isinstance(obj, Setter)  or isinstance(self, Setter)
         self.is_getter  = isinstance(obj, Getter)  or isinstance(self, Getter)
         self.is_deleter = isinstance(obj, Deleter) or isinstance(self, Deleter)
 
-        if isinstance(obj, (Setter, Getter, Deleter)):
-            self.obj = obj.obj
-        else:
-            self.obj = obj
+        self._obj = obj
 
-    def __ror__(self, other: Any) -> '_PropertyAccessModifierBase':
-        return self.__class__(other)
 
-class Setter(_PropertyAccessModifierBase):
-    pass
+    def __get__(self, owner_instance, owner_cls=None):
+        raise ValueError(
+            f"{owner_instance if owner_cls is None else owner_cls} is not gettable"
+        )
 
+    def __set__(self, owner_instance, value):
+        raise ValueError(
+            f"{owner_instance} is not settable"
+        )
 
-class Getter(_PropertyAccessModifierBase):
-    pass
+    def __delete__(self, owner_instance):
+        raise ValueError(
+            f"{owner_instance} is not deletable"
+        )
 
+class Setter(_PaamBaseDescriptor):
+    def __set__(self, owner_instance, value):
+        self._obj = value
 
-class Deleter(_PropertyAccessModifierBase):
-    pass
+class Getter(_PaamBaseDescriptor):
+    def __get__(self, owner_instance, owner_cls=None):
+        return self._obj
 
-class _PropertyAccessModifierFactoryBase:
+class Deleter(_PaamBaseDescriptor):
+    def __delete__(self, owner_instance):
+        del self._obj
+
+class _PropertyAccessModifierFactory:
     def __init__(self, cls: type) -> None:
         self.cls = cls
 
-    def __ror__(self, other: Any) -> _PropertyAccessModifierBase:
+    def __ror__(self, other: Any) -> _PaamBaseDescriptor:
+        if issubclass(other.__class__, _PaamBaseDescriptor):
+            class Both(self.cls, other.__class__):
+                pass
+            return Both(other._obj)
         return self.cls(other)
 
-SET = _PropertyAccessModifierFactoryBase(Setter)
-GET = _PropertyAccessModifierFactoryBase(Getter)
-DEL = _PropertyAccessModifierFactoryBase(Deleter)
-
-def property_access_mod_class(klass: type) -> type:
-    old_init = klass.__init__
-
-    def new_init(self, *args, **kwargs):
-        old_init(self, *args, **kwargs)
-        for k in dir(self):
-            v = getattr(self, k)
-            
-            if issubclass(type(v), _PropertyAccessModifierBase):
-                setter, getter, deleter = None, None, None
-                setattr(self, f'_{k}', v.obj)
-                if v.is_setter:
-                    _k = k
-                    setter = lambda obj, new: setattr(obj, f'_{_k}', new)
-                
-                if v.is_getter:
-                    _k = k
-                    getter = lambda obj: getattr(obj, f'_{_k}')
-                
-                if v.is_deleter:
-                    _k = k
-                    deleter = lambda obj: delattr(obj, f'_{_k}')
-
-                setattr(klass, k, property(getter, setter, deleter, f"Autogenerated by {__package__} for {klass}.{k}."))
-
-    klass.__init__ = new_init
-    return klass
+SET = _PropertyAccessModifierFactory(Setter)
+GET = _PropertyAccessModifierFactory(Getter)
+DEL = _PropertyAccessModifierFactory(Deleter)
+
+# read https://dev.to/mattconway1984/python-creating-instance-properties-2ej0
+# for more
+class PaamBase:
+    def __setattr__(self, attr_name: str, value: Any) -> None:
+        try:
+            attr = super().__getattribute__(attr_name) # avoid recursion this way
+        except AttributeError: # must be "normal" attribute
+            super().__setattr__(attr_name, value)
+        else:
+            if issubclass(type(attr), _PaamBaseDescriptor):
+                attr.__set__(self, value)
+            else:
+                super().__setattr__(attr_name, value) # if "normal" attribute
+
+    def __getattribute__(self, attr_name: str) -> Any:
+        attr = super().__getattribute__(attr_name)
+        if issubclass(type(attr), _PaamBaseDescriptor):
+            return attr.__get__(self, self.__class__)
+        return attr
+
+    def __delattr__(self, attr_name: str) -> None:
+        attr = super().__getattribute__(attr_name)
+        if issubclass(type(attr), _PaamBaseDescriptor):
+            attr.__delete__(self)
+        del attr