refactor table_name fetch for better readability

Author: wwwjfy

gino/declarative.py

@@ -152,12 +152,16 @@ def _init_table(cls, sub_cls):
         for each_cls in sub_cls.__mro__[::-1]:
             for k, v in getattr(each_cls, '__namespace__',
                                 each_cls.__dict__).items():
-                declared_callable_attr = callable(v) and \
-                                         getattr(v, '__declared_attr__', False)
-                if k != '__tablename__' and declared_callable_attr:
+                declared_callable_attr = (
+                    callable(v) and getattr(v, '__declared_attr__', False))
+                if k == '__tablename__':
+                    if declared_callable_attr:
+                        table_name = v(sub_cls)
+                    else:
+                        table_name = v
+                    continue
+                if declared_callable_attr:
                     v = updates[k] = v(sub_cls)
-                elif k == '__tablename__':
-                    table_name = v(sub_cls) if declared_callable_attr else v
                 if isinstance(v, sa.Column):
                     v = v.copy()
                     if not v.name: