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