misc: flake8 fixes

Author: enwask

devito/tools/abc.py

@@ -344,7 +344,9 @@ def get_or_create(self, key: KeyType,
                 obj = supplier()
 
                 # Listener for when the weak reference expires
-                def on_obj_destroyed(k: KeyType = key, f: Future[ReferenceType[ValueType]] = future):
+                def on_obj_destroyed(k: KeyType = key,
+                                     f: Future[ReferenceType[ValueType]] = future) \
+                        -> None:
                     with self._lock:
                         if self._futures.get(k, None) is f:
                             del self._futures[k]

tests/test_tools.py

@@ -257,7 +257,8 @@ def worker(key: int) -> CacheObject:
 
         with ThreadPoolExecutor(max_workers=num_threads) as executor:
             start_time = time.perf_counter()
-            results = list(executor.map(worker, (i % num_keys for i in range(num_threads))))
+            results = list(executor.map(worker, (i % num_keys
+                                                 for i in range(num_threads))))
             duration = time.perf_counter() - start_time
 
         # Ensure construction took a reasonable amount of time