[Python] Python Linked List - AttributeError: 'NoneType' object has no attribute 'get_data'...

I'm new to python and have been trying to learn simple data structures. I've been able to hack together some functions for a linked list and have been having trouble with my delete function. Heres list with the function in question and the test case: class Node: def init(self, initial_data): self.data = initial_data self.next = None

def get_data(self):
return self.data

def get_next(self):
return self.next

def set_data(self, new_data):
self.data = new_data

def set_next(self, new_next):
self.next = new_next


class LinkedList: def init(self): self.head = None

def __str__(self):
output_string = ''

current = self.head
while current is not None:
output_string += str(current.get_data())
next_node = current.get_next()
#gives the pointer to the next node i.e. the next node is that which is next to the current

if next_node is not None:
output_string += "->"

current = next_node

return output_string
#does not need to be changed for ordered linked list
def is_empty(self):
if self.head is None:
return True
else:
return False
def insert(self, data):
current = self.head
previous = None
stop = False
while current != None and not stop:
if current.get_data() > data:
stop = True
else:
previous = current
current = current.get_next()
temp = Node(data)
if previous == None:
temp.set_next(self.head)
self.head = temp
else:
temp.set_next(current)
previous.set_next(temp)



#does not need to be changed for ordered linked list
def size(self):
current = self.head
count = 0
while current != None:
count += 1
current = current.get_next()
return count
def search(self, item):
current = self.head
found = False
stop = False

while current is not None and not found and not stop:
if current.get_data() == item:
found = True

else:
current = current.get_next()
return found

def delete(self, item):
current = self.head
previous = None
found = False

while not found:
if current.get_data() == item:
found = True
else:
previous = current
current = current.get_next()

if previous is None:
self.head = current.get_next()
else:
previous.set_next(current.get_next())

def test_nonexistent():
my_list = LinkedList()
my_list.insert(31)
my_list.insert(77)
my_list.insert(17)
my_list.insert(93)
my_list.insert(26)
my_list.insert(54)
assert my_list.size() == 6
my_list.delete(77)
my_list.delete(1)
assert my_list.size() == 5


I get the error message

"AttributeError: 'NoneType' object has no attribute 'get_data' with delete Function"
​

I believe there is something wrong with the delete function as it can't handle a value thats isn't in the list, but I'm stumped as to how to get it to work at this point. Any help is appreciated!

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