This requires Python 3.7+, since I use the handy `dataclasses`

library.

I finally bothered to sit down and figure out how to properly write iterators in Python, and itâ€™s made implementing magic methods fun. I timed myself and all of these methods were written in 17 minutes.

By moving the iteration into syntactic sugar, we save ourselves a lot of pain and make the code a helluva lot clearer than the first time I wrote a linked list.

Notably, the ugly return tuple of `value, current node, next node`

makes
methods like `__add__`

and `last`

easy to implement.

```
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
from __future__ import annotations
from copy import deepcopy
from dataclasses import dataclass
from operator import eq, ge, gt, le, lt, ne
from typing import Callable, Dict, TypeVar
T = TypeVar("T")
@dataclass()
class LinkedList:
val: T
next: LinkedList = None
def __iter__(self):
return self._next()
def __next__(self):
yield from self._next()
def _next(self):
if self is not None:
curr = self
while curr is not None:
# this ugly return makes a lot of manipulation easier
yield (curr.val, curr, curr.next)
curr = curr.next
def __getitem__(self, idx: int) -> T:
for i, (x, curr, tail) in enumerate(self):
if i == idx:
return x
raise IndexError
def __len__(self):
return sum(1 for _ in self)
def __contains__(self, x: T) -> bool:
return any(x == y for y, *_ in self)
def __deepcopy__(self, memodict: Dict = {}):
l = LinkedList(self[0])
p = l
for x, *_ in self.next:
p.next = LinkedList(x)
p = p.next
return l
def _cmp(self, other, cmp: Callable, *, how_many: Callable = all):
return how_many(cmp(x, y) for (x, *_), (y, *_) in zip(self, other))
def __eq__(self, other: LinkedList) -> bool:
return self._cmp(other, eq)
def __ne__(self, other: LinkedList) -> bool:
return self._cmp(other, ne, how_many=any)
def __gt__(self, other: LinkedList) -> bool:
return self._cmp(other, gt)
def __ge__(self, other: LinkedList) -> bool:
return self._cmp(other, ge)
def __le__(self, other: LinkedList) -> bool:
return self._cmp(other, le)
def __lt__(self, other: LinkedList) -> bool:
return self._cmp(other, lt)
def __bool__(self):
return self is not None
def __reversed__(self):
"""Not lazy and not in place."""
if self is None:
return None
l = LinkedList(self[0])
for x, *_ in self.next:
l = LinkedList(x, l)
return l
def __add__(self, other: LinkedList) -> LinkedList:
head = deepcopy(self)
l = head
c = l.last()
c.next = deepcopy(other)
return head
def __iadd__(self, other: LinkedList) -> LinkedList:
l = self.last()
l.next = other
return self
def __str__(self) -> str:
return " -> ".join(str(x) for x, *_ in self)
def last(self) -> LinkedList:
# returns last node in list
for x, curr, tail in self:
if tail is None:
return curr
def __repr__(self) -> str:
return str(self)
```