Class DependenciesMapping

dask/_task_spec.py:1006–1044

class DependenciesMapping(MutableMapping):
    def __init__(self, dsk):
        self.dsk = dsk
        self._removed = set()
        # Set a copy of dsk to avoid dct resizing
        self._cache = dsk.copy()
        self._cache.clear()

    def __getitem__(self, key):
        if (val := self._cache.get(key)) is not None:
            return val
        else:
            v = self.dsk[key]
            try:
                deps = v.dependencies
            except AttributeError:
                from dask.core import get_dependencies

                deps = get_dependencies(self.dsk, task=v)

            if self._removed:
                # deps is a frozenset but for good measure, let's not use -= since
                # that _may_ perform an inplace mutation
                deps = deps - self._removed
            self._cache[key] = deps
            return deps

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

    def __delitem__(self, key: Any) -> None:
        self._cache.clear()
        self._removed.add(key)

    def __setitem__(self, key: Any, value: Any) -> None:
        raise NotImplementedError

    def __len__(self) -> int:
        return len(self.dsk)


class _DevNullMapping(MutableMapping):