Solution for Supermarket Queue Kata (https://www.codewars.com/kata/57b06f90e298a7b53d000a86) [edit: added comments for Pete education]

queue_kata.py

def queue_time(customers, n):
    # keep track of time
    wait = 0
    
    
    # pool of people currently checking out at a register
    checkers_out = []

    
    # how many customers to load into queue.
    # equals either the number of registers UNLESS
    # there are less customers than registers, in which case
    # all remaining customers are loaded up
    load = n if n < len(customers) else len(customers)

    
    # fill the checkout lanes!
    for i in range(load):
        checkers_out.append(customers[i])

        
    # take the customers in the registers out of the line
    customers = customers[load:]

    
    # we keep looping through until everyone has finished going through the registers and no one is left
    # checking stuff out
    while len(checkers_out) != 0:
        
        # so we get the lowest wait time of everyone currently checking out
        # and add that to how long we've been waiting
        wait += min(checkers_out)
        
        
        # then subtract that amount of time from everyone in the list.
        # that means whoever had the minimum wait time is now done!
        checkers_out = [i-min(checkers_out) for i in checkers_out]

        
        # go through the checkout registers. People who are done checking out
        # (ie, equal 0) are replaced with a new customer if there are anymore,
        # otherwise they'll be left at zero and removed after this loop
        for i in range(len(checkers_out)):
            if checkers_out[i] == 0:
                if len(customers) > 0:
                    checkers_out[i] = customers[0]
                    customers = customers[1:]

                    
        # get rid of everyone with zero wait time! (this happens
        # when there's no one in the queue to replace the current
        # people who've reached 0, but there are still others checking out.
        checkers_out = [i for i in checkers_out if i != 0]

        
    # all done, return our wait time!
    return wait


print(queue_time([2,2,3,3,4,4], 2)) #  prints 9! Rest of Codewars tests also pass <3