factory_boy fixture with a recursive factory

recursive_factory.py

import factory


class Comment:
    """A comment model can have replies, which are also Comments."""
    def __init__(self, author, text, replies=[]):
        self.author = author
        self.text = text
        self.replies = replies


class CommentFactory(factory.Factory):
    class Meta:
        model = Comment
        exclude = ("tree_depth",)

    author = factory.Sequence(lambda n: f"Comment Author Name {n}")
    text = factory.Sequence(lambda n: f"text {n}")

    @factory.LazyAttribute
    def replies(self):
        if self.tree_depth <= 0:
            return []
        else:
            num_children = 3
            return [
                CommentFactory.build(tree_depth=self.tree_depth - 1)
                for m in range(num_children)
            ]


comment_tree = CommentFactory(tree_depth=2)

assert len(comment_tree.replies) == 3
assert len(comment_tree.replies[0].replies) == 3
assert len(comment_tree.replies[0].replies[0].replies) == 0