# module_a.py
from multiprocessing import Event
from multiprocessing import Process
class BackgroundWorker(Process):
    """Create a worker background process."""
    def __init__(
        self,
        name: str,
        daemon: bool,
        contents: Any,
        event: Event,
    ) -> None:
        """Initialize the defaults."""
        self.contents: Any = contents
        self._event: Event = event
        super().__init__(name=name, daemon=daemon)
    def run(self) -> None:
        """Run the target function."""
        some code
        
        if self._event.wait(0.4):
        
        some code
        
        if self._event.is_set():
        	break
        	
       some code

# module_b.py
from multiprocessing import Event
event: Event = Event()
def cancel_task():
    event.set()     

error: Variable "multiprocessing.Event" is not valid as a type  [valid-type]
note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
error: Variable "multiprocessing.Event" is not valid as a type  [valid-type]
note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
error: Event? has no attribute "is_set"  [attr-defined]
error: Event? has no attribute "wait"  [attr-defined]

# module_a.py
from multiprocessing.synchronize import Event as EventClass
replace Event with EventClass
for eg, 
self._event: EventClass = event

# module_b.py
import multiprocessing
from multiprocessing.synchronize import Event as EventClass
event: EventClass = multiprocessing.Event()
def cancel_task():
    event.set()