I'm trying to understand python and OOP along with data structures
I'm now looking at the implementation of a binary search tree
here is the class for the node structure
class Node():
def __init__(self, data):
self.data = data
self.leftChild = None
self.rightChild = None
the developer of this code has created the insert feature in Node class and in another class called tree
here is what it looks like in the node class :
def insert(self, data):
if self.data == data:
return False
elif data < self.data:
if self.leftChild:
return self.leftChild.insert(data)
else:
self.leftChild = Node(data)
return True
else:
if self.rightChild:
return self.rightChild.insert(data)
else:
self.rightChild = Node(data)
return True
however, he created a function with the same name in the tree class which looks like this
class Tree():
def __init__(self):
self.root = None
def insert(self, data):
if self.root:
return self.root.insert(data)
else:
self.root = Node(data)
return True
I do have some questions at this point, why are there 2 functions with the same name? and when I try to execute one of them without the other on this code it shows an error
if __name__ == '__main__':
tree = Tree()
tree.insert(10)
why does he made instance for tree not for node ?
can someone please explain those concepts for me, thanks!
When you creating tree object it doesn't creating any node. It's just defining a root variable with None. Node is creating when you call tree.insert() method.
insert() method in Tree class is checking if root is None it creating a new Node. Otherwise it calling the insert method in Node class.
Why does he made instance for tree not for node ?
Because insert() method in Node class only handles the case where tree has atleast one node or tree is not empty. That's why he creating the instance of Tree.
Code with insert() method in Tree class:
class Node():
def __init__(self, data):
self.data = data
self.leftChild = None
self.rightChild = None
class Tree():
def __init__(self):
self.root = None
def insert(self, root, data):
if root is None:
self.root = Node(data)
elif root.data < data:
if root.rightChild is None:
root.rightChild = Node(data)
else:
self.insert(root.rightChild, data)
else:
if root.leftChild is None:
root.leftChild = Node(data)
else:
self.insert(root.leftChild, data)
Related
I have used a class for a program I have been working on. Unfortunately, I am struggling to return the value instead of the object memory location.
class Node:
def __init__(self, data):
self.data = data
class BinaryTree:
root = None
#classmethod
def InsertNode(cls, data):
newNode = Node(data)
if cls.root == None:
cls.root = newNode
return cls.root
else:
queue = []
queue.append(cls.root)
print(BinaryTree().InsertNode(4))
would return -> <__main__.Node object at 0x000001A8478CAE60>
Here is my code. I created a linked list manually to check if my method works or not. But the output I get is nothing. There is no output
class Node:
def __init__(self, data=None):
self.data = data
self.next = None
node1=Node(2)
node2=Node(4)
node3=Node(5)
node1.next=node2
node2.next=node3
a=node1
class MyList():
def __init__(self):
self.head=Node()
def isEmpty(self,a):
return self.head.next is None
hello=MyList()
print(hello.isEmpty(a))
In case you want to add data to LinkedList, you need to set the head of the list manually.
This code is probably what you want:
class Node:
def __init__(self, data=None):
self.data = data
self.next = None
node1=Node(2)
node2=Node(4)
node3=Node(5)
node1.next=node2
node2.next=node3
class MyList():
def __init__(self):
self.head=Node()
def isEmpty(self):
return self.head.data is None
hello=MyList()
print(hello.isEmpty())
new_hello = MyList()
new_hello.head=node1
print(new_hello.isEmpty())
Output
True
False
You never set the head node to point to another node in the way you're currently doing it (your head and "a" aren't actually the same node here). Pass in another variable as a node object to change this.
a = node1
class MyList():
def __init__(self, head):
self.head = head
def isEmpty(self):
return self.head is None # a linked list with a head is technically not empty
new_hello = MyList(a)
print (new_hello.isEmpty())
personally I would add an add_node(self, value) method and keep track of the end node as well, instead of doing it the way you are
For the code below I wrote for Binary Search Tree, I get the error delete_node(curr,value)
NameError: global name 'delete_node' is not defined. I am wondering why this will be the case for static method which is called from the instance method delete(self,value) . Why does it not work as a static method? I am calling it from a instance method 'delete' so does it does not require access to instance members explicitly.
class Node:
def __init__(self,value=None):
self.value = value
self.left = None
self.right = None
class BST:
def __init__(self,value=None):
self.root = Node(value)
#staticmethod
def delete_node(node,value):
if node is None:
return node
if value > node.value:
node.right = delete_node(node.right,value)
elif value < node.value:
node.left = delete_node(node.left,value)
else:
if node.left is None and node.right is None:
node = None
return None
elif node.left is None:
temp = node.right
node = None
return temp
elif node.right is None:
temp = node.left
node = None
return temp
else:
#min_value = get_min(node.right)
node.value = get_min(node.right)
node.right = delete_node(node.right,node.value)
def delete(self,value):
if self.root == None:
return
curr = self.root
delete_node(curr,value)
def get_min(node):
curr = node
while curr.left:
curr = curr.left
return curr.value
if __name__ == '__main__':
tree = BST(5)
tree.delete(5)
As others have eluded to, in order to call methods on a class object you have to specify the thing you're calling it on.
So where you use delete_node, you can use BST.delete_node since it's static. The design is a bit odd given a BST would normally be done as an object encapsulated completely, but this is your immediate problem.
If it's an instance method, then you would call self.delete_node
The design of your class seems confusing.
In python, when we define a staticmethod that means the class name is just something like namespace, you can not access any member of the class in the staticmethod.
If you want static methods in C#, try classmethod.
I recommend the popular question for classmethod vs staticmethod.
In the specific question, change your code like this:
class BST:
...
#staticmethod
def delete_node(node,value):
...
node.right = BST.delete_node(node.right,node.value)
def delete(self,value):
...
BST.delete_node(curr,value)
I have a LinkedList class that has close to 200 lines of code. I would like to make a new class LLCircular(LinkedList) by always making sure that any myLL.tail.next is myLL.head. I believe I would need to update append(), push(), remove(), etc. accordingly. Is there a way I can do this to keep the original LinkedList class intact? Maybe a decorator or some dunder method?
For brevity's sake, if reading the code, my push() method is just the inverse of append(). I also have a pop() and remove() method, which would need to be updated, if I just rewrite those methods. As I am trying to avoid that approach, I am not posting that part of the code.
class LinkedListNode:
def __init__(self, value, nextNode=None, prevNode=None):
self.value = value
self.next = nextNode
self.prev = prevNode
def __str__(self):
return str(self.value)
class LinkedList:
def __init__(self, values=None):
self.head = None
self.tail = None
if values is not None:
self.append(values)
def __str__(self):
values = [str(x) for x in self]
return ' -> '.join(values)
def append(self, value=None):
if value is None:
raise ValueError('ERROR: LinkedList.py: append() `value` PARAMETER MISSING')
if isinstance(value, list):
for v in value:
self.append(v)
return
elif self.head is None:
self.head = LinkedListNode(value)
self.tail = self.head
else:
''' We have existing nodes '''
''' Head.next is same '''
''' Tail is new node '''
self.tail.next = LinkedListNode(value, None, self.tail)
self.tail = self.tail.next
if self.head.next is None:
self.head.next = self.tail.prev
return self.tail
'''class LLCircular(LinkedList):'''
''' ??? '''
Test Code:
foo = LinkedList([1,2,3])
foo.tail.next = foo.head #My LL is now circular
cur = foo.head
i = 0
while cur:
print(cur)
cur = cur.next
i +=1
if i>9:
break
What you want is to call your LinkedList base class functions using the super keyword, and then add the slight modifications to the LLCircular class function, i.e:
class LLCircular(LinkedList):
def append(self, value=None):
super(LLCircular, self).append(value)
# In addition to having called the LinkedList append, now you want
# to make sure the tail is pointing at the head
self.tail.next = self.head
self.head.prev = self.tail
If it is "circular" it won't need a tail or head, would it?
Nor "append" makes sense - insert_after and insert_before methods should be enough - also, any node is a reference to the complete circular list, no need for different objects:
class Circular:
def __init__(self, value=None):
self.value = value
self.next = self
self.previous = self
def insert_after(self, value):
node = Circular(value)
node.next = self.next
node.previous = self
self.next.previous = node
self.next = node
def insert_before(self, value):
node = Circular(value)
node.next = self
node.previous = self.previous
self.previous.next = node
self.previous = node
def del_next(self):
self.next = self.next.next
self.next.previous = self
def __iter__(self):
cursor = self.next
yield self
while cursor != self:
yield cursor
cursor = cursor.next
def __len__(self):
return sum(1 for _ in self)
This is what I have so far. I am rather confused, what am I missing here? Is it standard to do Node.left = Node(5)? I think confusing. Should I have a addLeft function in the Tree class that does that for me? Little confused on standard tree implementation.
class Node:
def __init__(self,val):
self.val = val
self.right = None
self.left = None
class Tree:
def __init__(self):
self.root = None
t = Tree()
t.root = (Node(3))
print t.root.val