Please answer in Python code.

C-9.27 Show how to implement the FIFO queue ADT using only a priority queue and one additional integer instance variable.

class PriorityQueue: # Nested class to store priority queue items in a compositional way class _Item: __slots__ = "_key", "_value" def __init__(self, key, value): self._key = key self._value = value def __lt__(self, other): return self._key < other._key def is_empty(self): return len(self) == 0