10.2. While Patterns

• Until

• Infinite Loop

• Exit Flag

10.2.1. Until

Has stop conditions

>>> i = 0
>>>
>>> while i < 3:
...     print(i)
...     i += 1
0
1
2

10.2.2. Infinite Loop

Never ending loop. Used in servers to wait forever for incoming connections. Used in games for game logic.

>>> 
... while True:
...     print('hello')

10.2.3. Exit Flag

>>> abort = False
>>> i = 3
>>>
>>> while not abort:
...     print(i)
...     i -= 1
...
...     if i == 1:  # problem detected in the last second
...         print('Fuel leak detected. Abort, Abort, Abort!')
...         abort = True
3
2
Fuel leak detected. Abort, Abort, Abort!

In real life the exit flag pattern is useful if you have for example multi-threaded application. You can kill all the threads if any thread changes the flag. Multi-threaded apps will share this value and kill the loop as soon as the condition will be evaluated.