refactor(handler): Prevent circular imports with type hints

src/powerapi/actor/actor.py

@@ -28,19 +28,24 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 import logging
-import signal
 import multiprocessing
+import signal
 import sys
 import traceback
+from typing import TYPE_CHECKING
+
 import setproctitle
 
+from powerapi.actor.message import PoisonPillMessage
 from powerapi.exception import PowerAPIExceptionWithMessage, UnknownMessageTypeException
-from powerapi.actor.message import PoisonPillMessage, Message
-from powerapi.handler import HandlerException, Handler
-
+from powerapi.handler import HandlerException
 from .socket_interface import SocketInterface
 from .state import State
 
+if TYPE_CHECKING:
+    from powerapi.actor.message import Message
+    from powerapi.handler import Handler
+
 
 class InitializationException(PowerAPIExceptionWithMessage):
     """

src/powerapi/actor/state.py

@@ -27,10 +27,14 @@
 # OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+from typing import TYPE_CHECKING
+
 from powerapi.actor.supervisor import Supervisor
 from powerapi.exception import UnknownMessageTypeException
-from powerapi.handler import Handler
-from powerapi.actor.message import Message
+
+if TYPE_CHECKING:
+    from powerapi.handler import Handler
+    from powerapi.actor.message import Message
 
 
 class State:

src/powerapi/handler/handler.py

@@ -27,8 +27,12 @@
 # OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+from typing import TYPE_CHECKING
+
 from powerapi.exception import PowerAPIException, UnknownMessageTypeException
-from powerapi.actor.message import Message
+
+if TYPE_CHECKING:
+    from powerapi.actor.message import Message
 
 
 class HandlerException(PowerAPIException):