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'

55_Life/python/life.py

@@ -55,7 +55,7 @@ def main():
 
     pattern_height = len(pattern)
     pattern_width = 0
-    for line_num, line in pattern.items():
+    for _line_num, line in pattern.items():
         pattern_width = max(pattern_width, len(line))
 
     min_x = 11 - pattern_height // 2
@@ -94,7 +94,7 @@ def main():
 
         p = 0
         g += 1
-        for x in range(0, min_x):
+        for _ in range(min_x):
             print()
 
         for x in range(min_x, max_x + 1):
@@ -120,7 +120,7 @@ def main():
             print("".join(line))
 
         # line 295
-        for x in range(max_x + 1, MAX_HEIGHT):
+        for _ in range(max_x + 1, MAX_HEIGHT):
             print()
 
         print()