class Tracker:
    def __init__(self):
        self.returned_host_names = set()
        self.host_type_so_far = set()

    def allocate(self, host_type):
        self.counter = 0
        self.host_type_so_far.add(host_type)
        if host_type in self.host_type_so_far:
            self.counter+=1
        while True:
            maybe_hostname = host_type + str(self.counter)
            if maybe_hostname not in self.returned_host_names:
                self.returned_host_names.add(maybe_hostname)
                print(self.returned_host_names)
                return maybe_hostname
            else:
                self.counter+=1

    def deallocate(self, hostname):
        if hostname in self.returned_host_names:
            self.returned_host_names.remove(hostname)