Function _prepare_instrumentation

lib/sqlalchemy/orm/collections.py:778–823

Prepare a callable for future use as a collection class factory. Given a collection class factory (either a type or no-arg callable), return another factory that will produce compatible instances when called. This function is responsible for converting collection_class=list int

(
    factory: Union[Type[Collection[Any]], _CollectionFactoryType],
)

def _prepare_instrumentation(
    factory: Union[Type[Collection[Any]], _CollectionFactoryType],
) -> _CollectionFactoryType:
    """Prepare a callable for future use as a collection class factory.

    Given a collection class factory (either a type or no-arg callable),
    return another factory that will produce compatible instances when
    called.

    This function is responsible for converting collection_class=list
    into the run-time behavior of collection_class=InstrumentedList.

    """

    impl_factory: _CollectionFactoryType

    # Convert a builtin to 'Instrumented*'
    if factory in __canned_instrumentation:
        impl_factory = __canned_instrumentation[factory]
    else:
        impl_factory = cast(_CollectionFactoryType, factory)

    cls: Union[_CollectionFactoryType, Type[Collection[Any]]]

    # Create a specimen
    cls = type(impl_factory())

    # Did factory callable return a builtin?
    if cls in __canned_instrumentation:
        # if so, just convert.
        # in previous major releases, this codepath wasn't working and was
        # not covered by tests.   prior to that it supplied a "wrapper"
        # function that would return the class, though the rationale for this
        # case is not known
        impl_factory = __canned_instrumentation[cls]
        cls = type(impl_factory())

    # Instrument the class if needed.
    if __instrumentation_mutex.acquire():
        try:
            if getattr(cls, "_sa_instrumented", None) != id(cls):
                _instrument_class(cls)
        finally:
            __instrumentation_mutex.release()

    return impl_factory


def _instrument_class(cls):