Question

I am a newbie in Python. I can understand what a for loop does, but can’t really understand what a while loop does. I knew it does repeat something while the condition is true, easy to say, but it’s really hard to use it as far as I think.

Say, an example here:

while 1:
   rate(100) #what does this rate(100) do?
   try:
      'something'
   except:
      'something else'

I just can’t understand it. Help!

Answer 1

The example code you have provided is equivalent to this:

while True:
    rate(100) #what does this rate(100) do?
    try:
        'something'
    except:
        'something else'

In Python many expressions can be tested for truth (that is evaluate to True or False when used in conditions and logical operations). For example non-empty sequences or non-zero numbers as you have evaluate to True. So this loop will run forever or until some code explicitly breaks out of it. This is because the loop condition is hard-coded to True so will never evaluate to False to exit the loop.

The basic behaviour of the while loop in python is well explained in the Python Tutorial. Unless you have a more specific question I would suggest you start there. Other Python flow control constructs are also described there.