django_context_decorator.py

class context:
    """
    Use this class as a decorator around methods, properties, or cached
    properties to add the wrapped value (or result for callables) to
    the template context. Works for all Django View classes.
    Requires Python 3.6+
    """

    def __init__(self, func):
        self.func = func

    @staticmethod
    def _initialize_context_fields(cls):
        if getattr(cls, "_context_fields_owner", "") is cls:
            return

        cls._context_fields_owner = cls
        cls._context_fields = set()

        for parent in cls.mro()[1:]:
            cls._context_fields.update(getattr(parent, "_context_fields", set()))

    def __set_name__(self, owner, name):

        if hasattr(self.func, "__set_name__"):
            self.func.__set_name__(owner, name)

        self._initialize_context_fields(owner)
        owner._context_fields.add(name)

        if not getattr(owner, "get_context_data", False):

            def get_context_data(_self, **kwargs):
                return super(owner, _self).get_context_data(**kwargs)

            owner.get_context_data = get_context_data

        if not getattr(owner, "_context_patched", False):
            old_get_context_data = owner.get_context_data

            def new_get_context_data(_self, **kwargs):
                self._initialize_context_fields(type(_self))
                result = old_get_context_data(_self, **kwargs)
                for name in _self._context_fields:
                    attr = getattr(_self, name)
                    if callable(attr):
                        attr = attr()
                    result.setdefault(name, attr)
                return result

            owner.get_context_data = new_get_context_data
            owner._context_patched = True

    def __get__(self, instance, cls=None):
        return (
            self.func.__get__(instance, cls)
            if hasattr(self.func, "__get__")
            else self.func
        )