While loops
Usage in Python
- When do I use them?
While loops, like the ForLoop, are used for repeating sections of code - but unlike a for loop, the while loop will not run n times, but until a defined condition is met. As the for loop in Python is so powerful, while is rarely used, except in cases where a user's input is required, for example -
n=raw_input('Please enter\'hello\':')
while n.strip()!='hello':
n=raw_input('Please enter\'hello\':')
However, the problem with the above code is that it's wasteful. In fact, what you will see a lot of in Python is the following -
while True:
n=raw_input('Please enter\'hello\':')
if n.strip()=='hello':
break
As you can see, this compacts the whole thing into a piece of code managed entirely by the while loop. Having True as a condition ensures that the code runs until it's broken by n.strip() equalling 'hello'. Another version you may see of this type of loop uses 1 instead of True - this is exactly the same, though in Python 2.*, using while 1 is minutely faster, due to the ability to resign True to a different value.