[BUG] There is no mechanism for user to know the availability of cucim.CuImage

[gigony]

Describe the bug
Since v21.06.00, cuCIM silenced ImportError exception from from .clara import CuImage, __version__, cli
to support cucim.skimage package-only use case.

cucim/python/cucim/src/cucim/__init__.py

Line 44 in 3afa154

from .clara import CuImage, __version__, cli

try:
    import cupy
except ImportError:
    pass

try:
    from .clara import CuImage, __version__, cli
except ImportError:
    from ._version import get_versions
    __version__ = get_versions()['version']
    del get_versions
    del _version

That caused an issue on MONAI's tests because it wouldn't raise ImportError even if loading libcucim.so was failed, and it causes MONAI's optional_import() method to return True.

MONAI team (@wyli @drbeh) has the following workaround to check cucim.CuImage's availability.

drbeh/MONAI@a102ab7#diff-fcffca442c7cee4391ab58c3d2b71b80134da7621262457c69a3741308e156cd

Steps/Code to reproduce bug

• Install cuCIM v21.08.02 from PyPI
• import cucim
• img = cucim.CuImage("input.tif")

Expected behavior

• User may want to see error when import cucim if cucim.CuImage is not available.

Environment details (please complete the following information):

• Environment location: Docker
• Method of cuCIM install: PyPI

Additional context

We may want to expose a method in (cucim package) to to check if image loader(cucim.clara) or image processor(cucim.skimage, cucim.core) are available so that user can check the real availability.

• such as:
  • cucim.is_available() : check if all modules are available.
  • cucim.is_available("clara") : check if image loader-related modules are available.
  • cucim.is_available("skimage")
  • cucim.is_available("core")