Class Context

contextvars/__init__.py:24–64

class Context(collections.abc.Mapping, metaclass=ContextMeta):

    def __init__(self):
        self._data = immutables.Map()
        self._prev_context = None

    def run(self, callable, *args, **kwargs):
        if self._prev_context is not None:
            raise RuntimeError(
                'cannot enter context: {} is already entered'.format(self))

        self._prev_context = _get_context()
        try:
            _set_context(self)
            return callable(*args, **kwargs)
        finally:
            _set_context(self._prev_context)
            self._prev_context = None

    def copy(self):
        new = Context()
        new._data = self._data
        return new

    def __getitem__(self, var):
        if not isinstance(var, ContextVar):
            raise TypeError(
                "a ContextVar key was expected, got {!r}".format(var))
        return self._data[var]

    def __contains__(self, var):
        if not isinstance(var, ContextVar):
            raise TypeError(
                "a ContextVar key was expected, got {!r}".format(var))
        return var in self._data

    def __len__(self):
        return len(self._data)

    def __iter__(self):
        return iter(self._data)


class ContextVarMeta(type):