sentinel

Sentinel value for distinguishing “not provided” from None.

In many boto3 APIs, None is a meaningful value (e.g. region_name=None means “let boto3 resolve the region from the environment”). A plain None default therefore cannot tell whether the caller explicitly passed None or simply omitted the argument. The NOTHING sentinel fills that gap: any parameter whose default is NOTHING is treated as not provided and will be stripped out by resolve_kwargs() before forwarding to boto3.

NOTHING is also used as the “uninitialised” marker for lazy-loaded cached properties (e.g. _boto_ses_cache, _aws_account_id_cache), where the cached value itself could legitimately be None.

This module requires Python 3.10+. The previous implementation was borrowed from the boltons library circa 2014 and carried legacy Python 2 compatibility code (__nonzero__, sys._getframe for pickle support, dynamic inner classes). None of that machinery is needed in modern Python, so it has been replaced with the minimal implementation below.

boto_session_manager.sentinel.resolve_kwargs(_mapper: dict[str, str] | None = None, **kwargs) → dict[str, Any]

Return a dict of kwargs with all NOTHING values removed.

This lets callers write resolve_kwargs(region_name=self.region_name, ...) and get back only the keys that were explicitly provided.

Parameters:

_mapper – optional key-rename mapping, e.g. {"role_arn": "RoleArn"} translates the Python-style key to the AWS API name.