Because you're using while True and True is always equal to True, so this loop will never stop. You can do something like this:

while True:
    if P1 != cg2:
        cg2 = (mn+mx)/2 #guess based on middle of highest and lowest
        print "Computer has guessed: %d" %cg2
        previousguess.append(cg2)
        count2+=1

    else:
        print "The Computer has guessed it in %d times" %count2 
        break # use break to break the loop

Or just like this:

while P1 != cg2:
    cg2 = (mn+mx)/2 #guess based on middle of highest and lowest
    print "Computer has guessed: %d" %cg2
    previousguess.append(cg2)
    count2+=1

if P1 != cg2 is equal to False, this loop will terminated.

num_of_runs = sys.argv[1]

num_of_runs is a string at that stage.

while self.run_number <= self.num_of_runs:

You are comparing a string and an int here.

A simple way to fix this is to convert it to an int

num_of_runs = int(sysargv[1])

Another way to deal with this is to use argparser.

import argparse

parser = argparse.ArgumentParser(description='The program does bla and bla')
parser.add_argument(
    'my_int',
    type=int,
    help='an integer for the script'
)

args = parser.parse_args()
print args.my_int
print type(args.my_int)

Now if you execute the script like this:

./my_script.py 20

The output is:

20

Using argparser also gives you the -h option by default:

python my_script.py -h
usage: i.py [-h] my_int

The program does bla and bla

positional arguments:
  my_int      an integer for the script

optional arguments:
  -h, --help  show this help message and exit

For more information, have a look at the argparser documentation.

Note: The code I have used is from the argparser documentation, but has been slightly modified.

A while loop does not terminate when the condition becomes false. It terminates when it evaluates the condition and the condition is found to be false. That evaluation doesn't happen until the beginning of each loop iteration, not immediately after some event occurs that will allow the condition to become false.

A better way to write this loop is to simply use True as the condition, as it doesn't require you to initialize command to a known non-terminating value, then let a break statement somewhere the loop terminate the command when appropriate.

started = False
while True:
    command = input('Enter a Command: ').lower()
    if command == 'quit':
        break

    if command == 'start':
        if started:
            print("Car already Started! Let's go!")
        else:
            started = True
            print("Car Started.... Ready to Go!!!")
    elif command == 'stop':
        if not started:
            print('Car already stopped!')
        else:
            started = False
            print('Car stopped!')
    elif command == 'help':
        print(" 'start' - to start the car\n'stop' - to stop the car\n'quit' - to quit/close the game.")
    else:
        print('Sorry, I do not understand that!')

Of course, you don't need two separate if statements as I've shown here; you could combine them into one with if command == 'start' being the first elif clause of the combined if statement. But this provides an explicit boundary between "code that terminates the loop" and "code that allows the loop to continue".

The last line should read

y=y+1

Now it is not doing anything to y.

(A general tip for debugging: If your loop does not terminate, print out the loop value to see what is happening to it)

A common, but very frustrating and time-wasting typo, which can get even the best Python developers. Replace roll2 == random.randint(1,6) + random.randint(1,6) with roll2 = random.randint(1,6) + random.randint(1,6).

Also, I think you need roll2 != roll and roll2 != 7. From a stylistic point of view, it's better to omit the parenthesis around the statement evaluated in an if or while line.

Your loop has a slight amount of redundancy in it though. You check for roll2 being roll or 7 at the top of each loop and at the end of each loop. You could also consider trying this:

while True:
    # do everything in the same way as before

or

while roll2 != roll and roll2 != 7:
    # do stuff with the roll
    roll = random.randint(1,6) + random.randint(1,6)
return 1 if roll2 == roll else return 0 # a "ternary operator" in Python

login_or_register != 'login' or login_or_register != 'register' will always be True. You probably want to use a logical and:

while login_or_register != 'login' and login_or_register != 'register':
    # ....

this is b/c the while True does not end unless you use the keyword break wich breaks outside the loop and continues the code. the while True never ends

the while loop

while (condition):
    #code

never ends until the condition is False, witch would never be true for the True condition.

do your code should be:

game_list = ['0','1','2']

while True:

    position = myfunc()

    replacement(game_list,position)

    if not play_again():
         break
print(game_list)

or you could do:

game_list = ['0','1','2']

while play_again():

    position = myfunc()

    replacement(game_list,position)

print(game_list)

just indent your code correctly:

def determine_period(universe_array):
    period=0
    tmp=universe_array
    while True:
        tmp=apply_rules(tmp)#aplly_rules is a another function
        period+=1
        if numpy.array_equal(tmp,universe_array) is True:
            return period
        if period>12:  #i wrote this line to stop it..but seems its doesnt work....help..
            return 0
        else:   
            return period

You need to understand that the break statement in your example will exit the infinite loop you've created with while True. So when the break condition is True, the program will quit the infinite loop and continue to the next indented block. Since there is no following block in your code, the function ends and don't return anything. So I've fixed your code by replacing the break statement by a return statement.

Following your idea to use an infinite loop, this is the best way to write it:

def determine_period(universe_array):
    period=0
    tmp=universe_array
    while True:
        tmp=apply_rules(tmp)#aplly_rules is a another function
        period+=1
        if numpy.array_equal(tmp,universe_array) is True:
            break
        if period>12:  #i wrote this line to stop it..but seems its doesnt work....help..
            period = 0
            break

    return period

I think your understanding of what a while loop does is incorrect. The loop condition is only checked at the top of the loop, so, once before searchUnguided is called and never again (since you have a break statement after the last call). It is not tested in between the function calls.

What I think you want is something like this:

sky = searchUnguided(searchUnguided(inframe, skysearch, debug=debug)
if sky == "none":
    sky = searchPQ(ad, skysearch, maxpq, debug=debug)
    if sky == "none":
        sky = searchAB(ad, maxpq, debug=debug)
        # you may want another "if" here to do something else if sky is still "none"

It does terminate if your enter quit as the first number and anything else as the second number. But you still need to enter the second number, because it doesn't check what was entered until after both inputs.