iter states in states group (#666)

* iter states in states group

* fix type hint

* remove empty line

* add changes for doc

CHANGES/666.feature

@@ -0,0 +1,2 @@
+Ability to iterate over all states in StatesGroup.
+Aiogram already had in check for states group so this is relative feature.

aiogram/dispatcher/fsm/state.py

@@ -1,5 +1,5 @@
 import inspect
-from typing import Any, Optional, Tuple, Type, no_type_check
+from typing import Any, Iterator, Optional, Tuple, Type, no_type_check
 
 from ...types import TelegramObject
 
@@ -118,6 +118,9 @@ class StatesGroupMeta(type):
     def __str__(self) -> str:
         return f"<StatesGroup '{self.__full_group_name__}'>"
 
+    def __iter__(self) -> Iterator[State]:
+        return iter(self.__all_states__)
+
 
 class StatesGroup(metaclass=StatesGroupMeta):
     @classmethod

tests/test_dispatcher/test_fsm/test_state.py

@@ -150,6 +150,13 @@ class TestStatesGroup:
 
         assert MyGroup.MyNestedGroup.get_root() is MyGroup
 
+    def test_iterable(self):
+        class Group(StatesGroup):
+            x = State()
+            y = State()
+
+        assert set(Group) == {Group.x, Group.y}
+
     def test_empty_filter(self):
         class MyGroup(StatesGroup):
             pass