Django REST Framework context default value

drf_ctx_default.py

from operator import methodcaller
from django.utils.functional import cached_property
from typing import Union


class ContextDefaultValue:
    """>>> field = serializers.HiddenField(
       >>>    default=ContextDefaultValue("some_context_attr")
       >>> )"""
       
    def __init__(self, attr: Union[str, callable], default=None):
        self.context_attr = attr
        self.default = self.value = default

    def set_context(self, parent):
        self.value = self._context_getter(parent.context)

    def __call__(self):
        return self.value

    def __repr__(self):
        return f"{self.__class__.__name__}([{self.context_attr}, {self.default}])"

    @cached_property
    def _context_getter(self):
        if callable(self.context_attr):
            return self.context_attr

        return methodcaller("get", self.context_attr, self.default)