Allow <MyStruct*>obj as well; as there is no canonical PyObject

Cython/Compiler/ExprNodes.py

@@ -3939,7 +3939,8 @@ class TypecastNode(NewTempExprNode):
             if self.type.from_py_function:
                 self.operand = self.operand.coerce_to(self.type, env)
             elif self.type.is_ptr:
-                if not self.type.base_type.is_void:
+                base_type = self.type.base_type
+                if not base_type.is_void and not base_type.is_struct:
                     error(self.pos, "Python objects can only be cast to void*")
             else:
                 warning(self.pos, "No conversion from %s to %s, python object pointer used." % (self.type, self.operand.type))