def __init__(self): """ ------------------------------------------------------- Initializes an empty priority queue. Use: pq = Priority_Queue() ------------------------------------------------------- Returns: a new Priority_Queue object (Priority_Queue) ------------------------------------------------------- """ self._values = [] self._first = None defis_empty(self): """ ------------------------------------------------------- Determines if the priority queue is empty. Use: b = pq.is_empty() ------------------------------------------------------- Returns: True if priority queue is empty, False otherwise. ------------------------------------------------------- """ return len(self._values) == 0 def__len__(self): """ ------------------------------------------------------- Returns the length of the priority queue. Use: n = len(pq) ------------------------------------------------------- Returns: the number of values in the priority queue. ------------------------------------------------------- """ return len(self._values) definsert(self, value): """ ------------------------------------------------------- A copy of value is appended to the end of the the priority queue Python list, and _first is updated as appropriate to the index of value with the highest priority. Use: pq.insert(value) ------------------------------------------------------- Parameters: value - a data element (?) Returns: None ------------------------------------------------------- """ self._values.append(deepcopy(value)) # Determine whether new value has highest priority. ifself._first isNone: self._first = 0 elif value < self._values[self._first]: self._first = len(self._values) - 1 return def_set_first(self): """ ------------------------------------------------------- Private helper function to set the value of _first. _first is the index of the value with the highest priority in the priority queue. None if queue is empty. Use: self._set_first() ------------------------------------------------------- Returns: None ------------------------------------------------------- """ n = len(self._values) if n == 0: self._first = None else: self._first = 0 for i in range(1, n): ifself._values[i] < self._values[self._first]: self._first = i return defremove(self): """ ------------------------------------------------------- Removes and returns the highest priority value from the priority queue. Use: value = pq.remove() ------------------------------------------------------- Returns: value - the highest priority value in the priority queue - the value is removed from the priority queue. (?) ------------------------------------------------------- """ assert len(self._values) > 0, "Cannot remove from an empty priority queue" value = self._values.pop(self._first) # Find the value with the next highest priority. self._set_first() return value defpeek(self): """ ------------------------------------------------------- Peeks at the highest priority value of the priority queue. Use: v = pq.peek() ------------------------------------------------------- Returns: value - a copy of the highest priority value in the priority queue - the value is not removed from the priority queue. (?) ------------------------------------------------------- """ assert len(self._values) > 0, "Cannot peek at an empty priority queue" value = deepcopy(self._values[self._first]) return value def__iter__(self): """ FOR TESTING ONLY ------------------------------------------------------- Generates a Python iterator. Iterates through the priority queue from front to rear. Not in priority order. Use: for value in pq: ------------------------------------------------------- Returns: value - the next value in the priority queue (?) ------------------------------------------------------- """ for value inself._values: yield value
def __init__(self):
"""
-------------------------------------------------------
Initializes an empty priority queue.
Use: pq = Priority_Queue()
-------------------------------------------------------
Returns:
a new Priority_Queue object (Priority_Queue)
-------------------------------------------------------
"""
self._values = []
self._first = None
defis_empty(self):
"""
-------------------------------------------------------
Determines if the priority queue is empty.
Use: b = pq.is_empty()
-------------------------------------------------------
Returns:
True if priority queue is empty, False otherwise.
-------------------------------------------------------
"""
return len(self._values) == 0
def__len__(self):
"""
-------------------------------------------------------
Returns the length of the priority queue.
Use: n = len(pq)
-------------------------------------------------------
Returns:
the number of values in the priority queue.
-------------------------------------------------------
"""
return len(self._values)
definsert(self, value):
"""
-------------------------------------------------------
A copy of value is appended to the end of the the priority queue
Python list, and _first is updated as appropriate to the index of
value with the highest priority.
Use: pq.insert(value)
-------------------------------------------------------
Parameters:
value - a data element (?)
Returns:
None
-------------------------------------------------------
"""
self._values.append(deepcopy(value))
# Determine whether new value has highest priority.
ifself._first isNone:
self._first = 0
elif value < self._values[self._first]:
self._first = len(self._values) - 1
return
def_set_first(self):
"""
-------------------------------------------------------
Private helper function to set the value of _first.
_first is the index of the value with the highest
priority in the priority queue. None if queue is empty.
Use: self._set_first()
-------------------------------------------------------
Returns:
None
-------------------------------------------------------
"""
n = len(self._values)
if n == 0:
self._first = None
else:
self._first = 0
for i in range(1, n):
ifself._values[i] < self._values[self._first]:
self._first = i
return
defremove(self):
"""
-------------------------------------------------------
Removes and returns the highest priority value from the priority queue.
Use: value = pq.remove()
-------------------------------------------------------
Returns:
value - the highest priority value in the priority queue -
the value is removed from the priority queue. (?)
-------------------------------------------------------
"""
assert len(self._values) > 0, "Cannot remove from an empty priority queue"
value = self._values.pop(self._first)
# Find the value with the next highest priority.
self._set_first()
return value
defpeek(self):
"""
-------------------------------------------------------
Peeks at the highest priority value of the priority queue.
Use: v = pq.peek()
-------------------------------------------------------
Returns:
value - a copy of the highest priority value in the priority queue -
the value is not removed from the priority queue. (?)
-------------------------------------------------------
"""
assert len(self._values) > 0, "Cannot peek at an empty priority queue"
value = deepcopy(self._values[self._first])
return value
def__iter__(self):
"""
FOR TESTING ONLY
-------------------------------------------------------
Generates a Python iterator. Iterates through the priority queue
from front to rear. Not in priority order.
Use: for value in pq:
-------------------------------------------------------
Returns:
value - the next value in the priority queue (?)
-------------------------------------------------------
"""
for value inself._values:
yield value
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