满足条件时，Python while循环不会中断

Question

I'm just wondering why the loop doesn't break when it meets those conditions and filters over into my other functions? I fixed it by doing a while true loop and just breaking in each if statement, but I'd like to know what is wrong with doing this way.

def main_entrance():

print "\n\tYou are in the main entrance. It is a large room with" 
print "\ttwo doors, one to the left and one to the right. There"
print "\tis also a large windy stair case leading up to a second floor."
print "\n\tWhat are you going to do?\n"
print "\t #1 take the door on the left?"
print "\t #2 take the door on the right?"
print "\t #3 take the stairs to the second floor?"

choice = 0

#This seems to be the part that isn't working as I would expect it to.
# I have fixed it and have commented the fix out so that I can understand
# why this way isn't working.

#while True:

while (choice != 1) or (choice != 2) or (choice != 3):


    try:
        choice = int (raw_input ('> '))
        if (choice == 1):
            door_one_dinning_room()
            #break (should not need this break if choice is == 1, 2, 3)

        elif (choice == 2):
            door_two_study()
            #break

        elif (choice == 3):
            stairs_to_landing() 
            #there isn't anything in this function
            #but rather than breaking out from the program once it is 
            # called, but somehow this while loop is still running.

            #break

        else:
            print "You must pick one!"

    except:
        print "Please pick a number from 1-3"
        continue

Answer 1

Of course it doesn't break, your condition can never be false

(choice != 1) or (choice != 2) or (choice != 3)

Think about it for a minute, any selection of choice cannot make this expression false.

choice = 1

False or True or True --> True

choice = 2

True or False or True --> True

choice = 3

True or True or False --> True

Solution

You need to and the conditions together

(choice != 1) and (choice != 2) and (choice != 3)

Or better yet

while choice not in [1,2,3]

Answer 2

while (choice != 1) or (choice != 2) or (choice != 3):

This condition is always true. If your choice variable equals 1, then choice!=1 is false, but choice!=2 is true, so the whole condition is true. That is what or means.

You could put:

while (choice != 1) and (choice != 2) and (choice != 3):

or more succinctly:

while choice not in (1,2,3):