ch21 cleanup, f-strings, and pathlib

21-futures/demo_executor_map.py

@@ -24,7 +24,7 @@ def main():
     display('results:', results)  # <6>
     display('Waiting for individual results:')
     for i, result in enumerate(results):  # <7>
-        display('result {}: {}'.format(i, result))
+        display(f'result {i}: {result}')
 
 if __name__ == '__main__':
     main()