bug: unintended creation of wheel directory

[jiewpeng]

Describe the bug

When the user specifies Python options with wheels as empty list instead of None, bentoml will create the wheel directory, causing install.sh to fail because it tries to install *.whl from the wheels directory, but there are no wheel files inside.

This is normally not an issue because the user is expected to create a bentofile.yaml and use the bentoml CLI to build their bentos (and the user will typically not specify the wheels section at all if there are none), but in specific workflows where it is more convenient to use the bentoml Python interface to build bentos (e.g. when the user is using a notebook-centric environment like Databricks), the user may specify an empty list for wheels instead of None.

It is fairly simple to workaround this (we can specify None instead of empty list when calling bentoml.bentos.build()), but it would be nice if it could work with empty list as well. I can work on this, just let me know if it's ok to proceed.

if self.wheels is not None:
    bento_fs.makedirs(wheels_folder, recreate=True)
    for whl_file in self.wheels:  # pylint: disable=not-an-iterable
        whl_file = resolve_user_filepath(whl_file, build_ctx)
        copy_file_to_fs_folder(whl_file, bento_fs, wheels_folder)

if [ -d "$WHEELS_DIR" ]; then
    echo "Installing wheels packaged in Bento.."
    pip3 install "$WHEELS_DIR"/*.whl "${PIP_ARGS[@]}"
fi

I believe the check should be simplified to if self.wheels, so it covers the case of empty list as well.

To reproduce

No response

Expected behavior

No response

Environment

bentoml: 1.0.8 onwards
Python: 3.8

[aarnphm]

I think this can be fixed by simply change

if self.wheels is not None: ...

to

if self.wheels: ...

should cover your case.

The reason for checking is not None is that we want to avoid type coercion in Python. But I guess it is a thing in Python