Class LazyLocalNamespace

pydantic/_internal/_namespace_utils.py:66–103

A lazily evaluated mapping, to be used as the `locals` argument during annotations evaluation. While the [`eval`][eval] function expects a mapping as the `locals` argument, it only performs `__getitem__` calls. The [`Mapping`][collections.abc.Mapping] abstract base class is fully implem

# Note that this class is almost identical to `collections.ChainMap`, but need to enforce
# immutable mappings here:
class LazyLocalNamespace(Mapping[str, Any]):
    """A lazily evaluated mapping, to be used as the `locals` argument during annotations evaluation.

    While the [`eval`][eval] function expects a mapping as the `locals` argument, it only
    performs `__getitem__` calls. The [`Mapping`][collections.abc.Mapping] abstract base class
    is fully implemented only for type checking purposes.

    Args:
        *namespaces: The namespaces to consider, in ascending order of priority.

    Example:
        ```python {lint="skip" test="skip"}
        ns = LazyLocalNamespace({'a': 1, 'b': 2}, {'a': 3})
        ns['a']
        #> 3
        ns['b']
        #> 2
        ```
    """

    def __init__(self, *namespaces: MappingNamespace) -> None:
        self._namespaces = namespaces

    @cached_property
    def data(self) -> dict[str, Any]:
        return {k: v for ns in self._namespaces for k, v in ns.items()}

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

    def __getitem__(self, key: str) -> Any:
        return self.data[key]

    def __contains__(self, key: object) -> bool:
        return key in self.data

    def __iter__(self) -> Iterator[str]:
        return iter(self.data)


def ns_for_function(obj: Callable[..., Any], parent_namespace: MappingNamespace | None = None) -> NamespacesTuple: