StreamSource

def as_dict(self) -> Dict[str, object]:
    """Return the object converted into an API-friendly dict.
    """
    result = {}
    for field in fields(self):
        val = getattr(self, field.name)
        if val is None:
            continue
        if isinstance(val, Base):
            val = val.as_dict()
        result[field.name] = val
    return result

def evolve(self: _B, **params) -> _B:
    """Return a copy of the instance with the passed values replaced.
    """
    return replace(self, **params)

@classmethod
def from_response(cls, resp: Dict[str, Any]):
    cls._convert(resp, 'external', ExternalStream)
    return super().from_response(resp)