Use break to exit a loop:

while True:
    ser = serial.Serial("/dev/ttyUSB0", 4800, timeout =1)
    checking = ser.readline();
    if checking.find(",,,,"):
        print "not locked yet"
    else:
        print "locked and loaded"
        break

The True and False line didn't do anything in your code; they are just referencing the built-in boolean values without assigning them anywhere.

Yes!

Once the condition has been met, use break:

while True:
    someVar = str.lower(input())

    if someVar == 'yes':
        someVar = True
        break
    if someVar == 'no':
        someVar = False
        break

You can also use while False with:

met = True

while met:

   someVar = str.lower(input())

   if someVar == 'yes':
        someVar = True
        break
    if someVar == 'no':
        someVar = False
        break

Since all strings are True, use another variable to store either True or False. Once met is false, then the loop will break.

Have a look on a code below:

def repeat():
    correct_value = False

    # while not False so the correct_value = True
    # so it is an equivalent of -> while True:
    # while True will always run
    while not correct_value:
        try:
            guess = int(input())
        except ValueError:
            print("Please Enter a Number")
        else:
            correct_value = True
    return guess

Why does "while not false" even loops in the first place?
It loops because of the double negation which is always True.

And what's the actual really keeps the loop running?
Exactly the same while not False, which results in while True

If you want 'while false' functionality, you need not. Try while not fn: instead.

while True means loop forever. The while statement takes an expression and executes the loop body while the expression evaluates to (boolean) "true". True always evaluates to boolean "true" and thus executes the loop body indefinitely. It's an idiom that you'll just get used to eventually! Most languages you're likely to encounter have equivalent idioms.

Note that most languages usually have some mechanism for breaking out of the loop early. In the case of Python it's the break statement in the cmd == 'e' case of the sample in your question.

Since your while not pair: loop did not work, you have found an important difference: pair == False only tests true if pair is set to 0 or False (the only two values that test as equal to False), while while not pair tests for any truth value (inverting that value).

You appear to have assigned some other value to pair that is neither of those two values causing the behaviour to change (a truthy value to break out early, or a falsey value to keep the loop going longer than expected).

It is that difference that is one of the reasons why the Python style guide recommends you always use if true_expression or if not false_expression rather than use == True or == False:

• Don't compare boolean values to True or False using ==.

  Yes: if greeting:
  No: if greeting == True:
  Worse: if greeting is True:

Last but not least, for a while ...: loop that simply tests against a single boolean flag (while flag: or while not pair:), consider using while True: and break instead. So rather than do:

flag = True
while flag:
    # ...
    if condition:
        flag = False

do this instead:

while True:
    # ...
    if condition:
        break