Singly linked list implementation in python 3

Question

I have implemented a Singly linked list. It works well. But if you think something needs to be improved, say it. This code was tested in Python 3.7.4.

class Node(object):
 def __init__(self, data):
 self.data = data
 self.nextNode = None
class LinkedList(object):
 def __init__(self):
 self.head = None
 self.size = 0
 # O(1) !!! 
 def insertStart(self, data):
 self.size = self.size + 1
 newNode = Node(data)
 if not self.head:
 self.head = newNode
 else:
 newNode.nextNode = self.head
 self.head = newNode
 def remove(self, data):
 if self.head is None:
 return
 self.size = self.size - 1
 currentNode = self.head
 previousNode = None
 while currentNode.data != data:
 previousNode = currentNode
 currentNode = currentNode.nextNode
 if previousNode is None:
 self.head = currentNode.nextNode
 else:
 previousNode.nextNode = currentNode.nextNode 
 # O(1) 
 def size1(self):
 return self.size
 # O(N)
 def insertEnd(self, data):
 self.size = self.size + 1
 newNode = Node(data)
 actualNode = self.head
 while actualNode.nextNode is not None:
 actualNode = actualNode.nextNode
 actualNode.nextNode = newNode
 def traverseList(self):
 actualNode = self.head
 while actualNode is not None:
 print(actualNode.data)
 actualNode = actualNode.nextNode

• AlexV: You added the unit-testing tag, but I cannot see any unit tests in your code.

Answer 1

You are missing several important things for this code:

Type Annotations

Python 3.7 supports type annotations. Especially for a container class like this, you should fully use them.

Initializer parameters

Python containers generally all provide builder methods or class initializer functions that take other containers and use their contents. Consider:

• dict(iterable,**kwarg)
• list(iterable)
• set(iterable)
• str(object=b'', encoding='utf-8', errors='strict')
• tuple(iterable)

If you're writing a Python container, you need to conform to expectations. I expect to be able to initialize the container when I create it.

Protocols & Magic methods

Python has a well-established set of protocols for implementing containers. You just have to decide what kind of container you're writing.

I would suggest that a singly-linked list is an Iterable, a Sequence, a MutableSequence and possibly a Set type.

• Reinderien: The type annotations comment is certainly true, but a more direct reference to documentation is important for the uninitiated, if not an example applied to the code.