I’m creating a List class in python (a List like java lists) using generics. The class node is also generic and I’m creating the getters and setters methods for the prev and next node. I was wondering how could I return a type like the class node itself?
This is my progress:
from typing import Generic, TypeVar
T = TypeVar('T')
class Node(Generic[T]):
''' Generic class Node. It models a node for a linked list. '''
def __init__(self, element: T) -> None:
''' Constructor. It recives an element of type T.'''
self.element = element
self.next = None
self.prev = None
def get_item(self) -> T:
''' Returns the item in the node.'''
return self.element
def get_prev(self) -> #What is the type I should return here?:
''' Returns the previous node.'''
return self.prev
def get_next(self) -> #What is the type I should return here?:
''' Return the next node.'''
return self.next
def set_prev(self, prev) -> None:
''' Changes the previous element to the specified node.'''
self.prev = prev
def set_next(self, next) -> None:
''' Changes the next element to the specified node.'''
self.next = next
I’ve tried with
def get_prev(self) -> Node[T]:
''' Returns the previous node.'''
return self.prev
def get_next(self) -> Node[T]:
''' Return the next node.'''
return self.next
But it gives me the error
Traceback (most recent call last):
File "List.py", line 5, in <module>
class Node(Generic[T]):
File "List.py", line 18, in Node
def get_prev(self) -> Node[T]:
NameError: name 'Node' is not defined
Answers:
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Method 1
I think the newest Python versions have the capability of self-referencing classes in type annotations (here, get_prev‘s return type Node that is currently being defined).
Older Python versions, down to 3.7, still support it by adding:
from __future__ import annotations
see: https://peps.python.org/pep-0563/#enabling-the-future-behavior-in-python-3-7
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