How to build a linked list in python

[FallenApple]

Homework Statement

[/B]
Build a linked list with values of 1, 2 and 3

The Attempt at a Solution

class ListNode(object):
    def _init_(self,x):
      self.val=x
      self.next=None
 
 
 
 
 
root=ListNode(1)  
root.next=ListNode(2)
root.next.next=ListNode(3)

print(root.val)

I keep getting error object takes no parameters

 

[QuantumQuest]

You should rethink what classes you need and what operations should be done on the list (for instance to add a node).

 

[Dick]

You need two underscores. The initializer of a class should be __init__, not _init_.

 

[FallenApple]

You should rethink what classes you need and what operations should be done on the list (for instance to add a node).

I thought the root, root.next, and root.next.next connects the nodes while the right hand side of the equation declares them.

 

[FallenApple]

You need two underscores. The initializer of a class should be __init__, not _init_.

I tried that but I still get "error name root is not defined"

 

[Dick]

I tried that but I still get "error name root is not defined"

With the double underscores it works for me. It prints '1'. Can you repost the corrected code??

 

[FallenApple]

With the double underscores it works for me. It prints '1'. Can you repost the corrected code??

class ListNode(object):
    def __init__(self,x):
      self.val=x
      self.next=None
 
   
   
    root=ListNode(1)
    root.next=ListNode(2)
    root.next.next=ListNode(3)
   
   
   
   
print(root.val)

I ran it using https://repl.it/

 

[Dick]

class ListNode(object):
    def __init__(self,x):
      self.val=x
      self.next=None
 
  
  
    root=ListNode(1)
    root.next=ListNode(2)
    root.next.next=ListNode(3)
  
  
  
  
print(root.val)

I ran it using https://repl.it/

That's because the indentation levels on the lines using ListNode makes them part of the class definition. Indent them at the same level as the print statement. White spaces is syntax in Python.

 

[FallenApple]

That's because the indentation levels on the lines using ListNode makes them part of the class definition. Indent them at the same level as the print statement. White spaces is syntax in Python.

Got it! thanks. I'm used to using languages such as r or c++ where that isn't much of an issue because of curly braces.

 

[QuantumQuest]

I thought the root, root.next, and root.next.next connects the nodes while the right hand side of the equation declares them.

Be careful, this is an assignment - not an equation, that assigns the right hand side (return of call to class constructor) to the left hand side (node creation). What I meant in #2 is a general comment as I saw the code i.e. it would be better in my opinion to first create a separate class for linked list, another one for ListNode and you could add an operation like add_ListNode and then spot the error(s).