How does this while loop work?

Question

Hoping someone can explain what's going on with this while loop.

x=deque([(1,2,3)])
while x:
    a,b,c = x.popleft()
    do stuff with values in x
    x.append((d,e,f))

I get that x is a deque with 3 items which are constantly being replaced by new values. But I've never encountered a while loop without some kind of condition. How will the loop know when to stop?

Answer 1

x=deque([(1,2,3)]) # create new deque
while x: # while not empty
    a,b,c = x.popleft() # pop values and assign them to a and b and c
    # do stuff with values in x - this is comment too
    x.append((d,e,f)) # assumes produced new values d 
                      #and e and f and pushes them to x
# this assumes there is always d and e and f values and stays forever in loop 

as explained in here Python 2.7: How to check if a deque is empty?

Answer 2

As written, the code is an infinite loop because it adds data at the same rate as it is being removed.

If the size was being whittled down, the while x would terminate the loop when the deque was empty.

Answer 3

The boolean value of x=deque([(1,2,3)]) is True because it has a value and is not equal to None . This is an infite loop like while 1: or while True: .

For this loop to end you would either have to use a break when a condition is met or set x = None to break the loop