Data Structure (Swap Nodes)

class Node:
    def __init__(self,data):
        self.data=data
        self.next= None



class linked_list:
    def __init__(self):
        self.head = None
    def print_node(self):
        current_node=self.head
        while current_node:
            print(current_node.data)
            current_node=current_node.next
    def append(self,data):
        new_node=Node(data)
        if self.head is None:
            self.head=new_node
            return

        last_node=self.head
        while last_node.next:
            last_node=last_node.next
        last_node.next=new_node



    def swap_nodes(self,key1,key2):
        if key1==key2:
            return
        previous_node1=None
        current_node1=self.head
        while current_node1 and current_node1!= key1:
            previous_node1=current_node1
            current_node1=current_node1.next

        previous_node2= None
        current_node2=self.head
        while current_node2 and current_node2!=key2:
            previous_node2=current_node2
            current_node2=current_node2.next

        if not current_node1 or not current_node2:
            return
        if previous_node1:
            previous_node1.next=current_node2
        else:
            self.head=current_node2
        if previous_node2:
            previous_node2.next=current_node1
        else:
            self.head=current_node1

        current_node1.next,current_node2.next=current_node2.next,current_node1.next






llistt=linked_list()
llistt.append('a')
llistt.append("b")
llistt.append('c')
llistt.append("d")


#llistt.delete_middle_node("b")
#llistt.print_node()
#print(llistt.len_iterative())
llistt.swap_nodes("a","b")
llistt.print_node()