I am trying to implement min and max into a queue:
class Queue:
"""Queue implementation as a list"""
def __init__(self):
"""Create new queue"""
self._items = []
def is_empty(self):
"""Check if the queue is empty"""
return not bool(self._items)
def enqueue(self, item):
"""Add an item to the queue"""
self._items.insert(0, item)
def dequeue(self):
"""Remove an item from the queue"""
return self._items.pop()
def size(self):
"""Get the number of items in the queue"""
return len(self._items)
def find_min(self):
return sorted(self._items[0]) <=min
def find_max(self):
return sorted(self._items[-1]) <=max
When I try to call find_max I seem to be run into this error:
TypeError: 'int' object is not iterable
Im not entirely sure how to fix this, or if the code is just wack.
Related
Actually my sort algorithm works, but there is a problem.
I have a class namely SortedItem which includes
def __init__(self, point, cost):
self.coordinate = point
self.cost = cost
and I have also priority queue which sorts the this SortedItem by its cost:
class PriorityQueue:
def __init__(self):
self.items = []
def isEmpty(self):
return self.items == []
def sortComparatorByCost(self, item):
return item.cost
def enqueue(self, item):
self.items.append(item)
self.items.sort(key=self.sortComparatorByCost, reverse=True)
def dequeue(self):
return self.items.pop()
def returnQueueAsString(self):
queue_str = ""
for eachItem in self.items:
queue_str += str(eachItem) + " "
return queue_str
def isQueueContainsElement(self, element):
for eachElement in self.items:
if eachElement[0] == element:
return True
return False
The problem occurs here:
- I have defined some order to add queue. Let's say I am adding this objects to the queue:
obj1 = SortedItem((1,0), 10))
queue.enqueue(obj1)
obj2 = SortedItem((2,0), 15))
queue.enqueue(obj2)
obj3 = SortedItem((2,1), 15))
queue.enqueue(obj3)
Now I have to get objects from queue in this order (obj1, obj2, obj3).
However python built-in sort function sort these objects like this: (obj1, obj3, obj2) (because obj2 and obj3 has the same cost)
How can i solve this issue. I mean If 2 objects cost is the same, I should get the first added one.
Note that: I have just created a simple example of my problem. If you try this code you may get the objects in this order: obj1, obj2, obj3
Instead of sorting the items in reverse order and removing them from the right,
def enqueue(self, item):
self.items.append(item)
self.items.sort(key=self.sortComparatorByCost, reverse=True)
def dequeue(self):
return self.items.pop()
you could remove them from the left. That would avoid reversing the order of insertion of the items with the same cost.
def enqueue(self, item):
self.items.append(item)
self.items.sort(key=self.sortComparatorByCost)
def dequeue(self):
return self.items.pop(0)
Removing items from the beginning of a list is not efficient, however, so you could better use a deque (replacing pop(0) by popleft()) to fix that. A deque on the other hand, has no in-place sort() method, so would need to replace self.items.sort() by self.items = deque(sorted(self.items)) as well.
class Queue:
def __init__(self):
self.items = []
def isEmpty(self):
return self.items == []
def enqueue(self, item):
self.items.append(item)
def dequeue(self):
if self.items == []:
raise IndexError('The queue is empty.')
return self.items.pop()
def size(self):
return len(self.items)
def __str__(self):
return "Queue: " + (str(self.items))
def enqueue_list(self, list):
for i in list:
self.items.append(i)
return self.items
def splice(self, second_queue):
for i in second_queue:
self.items.enqueue(i)
return self.items
Hi there,
What I am trying to do is at the bottom in the splice method. I want to iterate through a second queue and add it to the end of the original one. I can't find out how I can iterate through a queue without causing an error however. Should I change second_queue into a list somehow first?
Original exception was:
Traceback (most recent call last):
File "prog.python3", line 74, in <module>
my_queue.splice(another_queue)
File "prog.python3", line 28, in splice
for i in second_queue:
TypeError: 'Queue' object is not iterable
Instances of your class Queue are not iterable.
They hold a list items, but Python does not know that it should iterate over that list when you employ a for loop over a Queue instance.
To delegate the iteration to the wrapped list, simply add a method
def __iter__(self):
return iter(self.items)
Demo with fixed class:
>>> q = Queue()
>>> q.enqueue(1)
>>> q.enqueue(2)
>>> q.items
[1, 2]
>>>
>>> for item in q:
... print(item)
...
1
2
Why this given error in Eclispse??
I run this program in IDlE python it works perfect
class Queue:
def _init_(self):
self.items = []
def isEmpty(self):
return self.items == []
def enqueue(self, item):
self.items.insert(0,item)
def dequeue(self):
return self.items.pop()
def size(self):
return len(self.items)
q = Queue()
q.enqueue(1)
q.enqueue(2)
q.enqueue(3)
print(q.size())
I'm doing some basic Python programming practice exercises and tried to implement a queue (using lists). Unfortunately, I'm getting behavior for my isempty() function that I don't understand. When running the code below, the last two lines give different answers: A yields False, while B yields True. Why doesn't A also yield False?
class Queue:
def __init__(self):
self.items = []
def push(self,item):
self.items.insert(0,item)
def pop(self):
return self.items.pop()
def size(self):
return len(self.items)
def isempty(self):
return self.size == 0
q = Queue()
q.push("a")
q.push("b")
print(q.pop())
print(q.isempty())
print(q.pop())
print(q.isempty()) # shouldn't this (A)...
print(q.size()==0) # ...and this (B) yield the same answer?
Just change your isempty() method to:
def isempty(self):
return self.size() == 0
Your implementation of Queue.isempty() is checking to see if the method size is equal to the integer 0, which will never be true.
class Queue:
def __init__(self):
self.items = []
def push(self,item):
self.items.insert(0,item)
def pop(self):
return self.items.pop()
def size(self):
return len(self.items)
def isempty(self):
return self.size == 0
q = Queue()
print(q.size)
Produces:
<bound method Queue.size of <__main__.Queue object at 0x02F4EA10>>
The easiest solution is to use Christopher Shroba's suggestion to modify your Queue.isempty() implementation to use the list's size method.
Ok so im trying to input a word in a stack and I want to print all of them after I input a string. So I can only print them one at a time. I tried using a for loop outside but Stacks are apparently not iterable. So I iterating it inside the stack. It still is not working.
class Stack:
def __init__(self):
self.items = []
def push(self,items):
self.items.insert(0,items)
def pop(self):
for x in self.items:
print( self.items.pop(0))
def show(self):
print (self.items)
s = Stack()
s.show()
placed = input("enter")
item = s.pop()
print(item, "is on top", s)
Give your Stack class a __len__ method, this will make testing if the stack is empty easier:
class Stack:
def __init__(self):
self.items = []
def push(self,item):
self.items.append(item)
def pop(self):
return self.items.pop()
def show(self):
print (self.items)
def __len__(self):
return len(self.items)
stack = Stack()
stack.push('World!')
stack.push('Hello')
while stack: # tests the length through __len__
print(stack.pop())
Note that I simply .append() to the end of the .items list, then later on .pop() (no arguments) again, removing from the end of the list.
To make your class an iterable type, you'd need to add at least an __iter__ method, optionally together with a .__next__() method:
class Stack:
# rest elided
def __iter__(self):
return self
def next(self):
try:
return self.items.pop()
except IndexError: # empty
raise StopIteration # signal iterator is done