itertools bfs

bfs.py

from itertools import zip_longest, chain
from dataclasses import dataclass, field

@dataclass
class Tree:
    value: any
    children: list = field(default_factory=list)
    
    def levels(self):
        yield [self]
        for level in zip_longest(*(c.levels() for c in self.children), fillvalue=()):
            yield chain.from_iterable(level)

    def bfs(self):
        return chain.from_iterable(self.levels())

tree = Tree(1, [
    Tree(2),
    Tree(3, [
        Tree(4),
        Tree(5, [
            Tree("hi"),
            Tree("bye")
        ])
    ]),
    Tree(6, [
        Tree("LOL")
    ])
])

for subtree in tree.bfs():
    print(subtree.value)