Clean Code: Python

Fix issues found by flake8-bugbear:

* Unused loop variables
* assert statements in non-test code
* mixing test code with production code
* mark one excessive test which takes ~10min to run
  as 'slow'

47_Hi-Lo/python/hilo.py

@@ -21,7 +21,7 @@ def play():
         secret = random.randint(1, 100)
         guessed_correctly = False
 
-        for attempt in range(MAX_ATTEMPTS):
+        for _attempt in range(MAX_ATTEMPTS):
             print("YOUR GUESS", end=QUESTION_PROMPT)
             guess = int(input())