class PositionalQueue(object):
""" A queue implementation based on positional list.
With enqueue returning a position instance and support for a new method,
delete(p), that removes the element associated with position p from the
queue.
"""
def __init__(self):
self._data = PositionalList()
def __len__(self):
""" Length method."""
return len(self._data)
def is_empty(self):
""" check if the queue is empty or not."""
return len(self._data) == 0
def first(self):
""" get the first element of the queue."""
if self._data.is_empty():
raise Empty('The queue is empty')
return self._data.first().element()
def enqueue(self, e):
""" add an element to the end of the queue.
:return: the Position of the element just be enqueued.
"""
return self._data.add_last(e)
def dequeue(self):
""" remove the first element of the queue."""
self._data.delete(self._data.first())
def delete(self, p):
""" Delete the element associated with position p."""
self._data.delete(p)
def __repr__(self):
return str(self._data)
