• One small mistake and your program might run forever.
  • A good class to use to test while loops in Python is the datetime class. 
    from datetime import datetime
  • while loops
  • We can get the current time using: 
    datetime.now()
  • Can get the exact seconds, for example with: 
    datetime.now().second
  • An example while loop that waits for 2 seconds and then prints out a message: 
    wait_until = datetime.now().second + 2
while datetime.now().second != wait_until:
   print('Still waiting!')
print(f'We are at {wait_until} seconds!')
  • The f above is an f statement
  • To make the above better and more efficient, we are going to use the pass statement. ``` wait_until = datetime.now().second + 2

while datetime.now().second != wait_until: pass

print(f’We are at {wait_until} seconds!’)

* The `pass` statement says "nothing to see here, move along" and it does preserve the indentation (required for while loops) and is a great placeholder.
	* If you are writing a function or a class definition and don't want to fill it in yet, you can just write `pass`.
* Another way to write this is using the `break` statement:

wait_until = datetime.now().second + 2

Generally shouldn’t use while True

while True: if datetime.now().second == wait_until: print(f’We are at {wait_until} seconds!’) break

* The `break` statement breaks out of the current loop that it is in.
* The `break` statement goes up the lines of code and goes to the `print` and says, "is this a loop", then goes further up at the `if` and says "is this a loop?", nope, and goes to the `while` and the break out of it and exits the loop.
	* The `break` statement will only break out of the first `while` loop that is encounters.
* As an example, this would not work:

while True: while datetime.now().second == wait_until: print(f’We are at {wait_until} seconds!’) break

* The `break` statement would only break out of `while datetime.now().second == wait_until:`
* The final `control statement` for loops is `continue`
	* This skips any lines that follow it inside of the `while` loop.
* For example:

wait_until = datetime.now().second + 2

while datetime.now().second != wait_until: continue print(‘Still waiting!’)

print(f’We are at {wait_until} seconds!’)

* The above `continue` will eventually exit the loop and print the following statement: `print(f'We are at {wait_until} seconds!')`
* It is not a common usage of `continue`.
	* Usually you see a `continue` statement used inside an `if` statement to prevent the code in the loop for executing, if some condition is met.
	* An example is:

wait_until = datetime.now().second + 2

while True: if datetime.now().second < wait_until: continue break

print(f’We are at {wait_until} seconds!’) ```

  • When the above continue statement is met, it skips all else in the loop, which is the break statement. Once the if datetime.now().second < wait_until: is no longer true, the continuestatement is no longer hit and it goes to the break statement.
  • continue and break are not techinically and logically necessary. They can help you rearrange and rewrite code for other programmers to read.

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