# Pretty print Linked List in Python class Node:    def __init__(self, val=None):        self.val = val        self.next = None    class LinkedList:    def __init__(self, head=None):        self.head = head      def __str__(self):                # defining a blank res variable        res = ""                  # initializing ptr to head        ptr = self.head                 # traversing and adding it to res        while ptr:            res += str(ptr.val) + ", "            ptr = ptr.next         # removing trailing commas        res = res.strip(", ")                  # chen checking if         # anything is present in res or not        if len(res):            return "[" + res + "]"        else:            return "[]"    if __name__ == "__main__":        # defining linked list    ll = LinkedList()      # defining nodes    node1 = Node(10)    node2 = Node(15)    node3 = Node(20)      # connecting the nodes    ll.head = node1    node1.next = node2    node2.next = node3          # when print is called, by default     #it calls the __str__ method    print(ll)