A code snippet to import optional cupy

import_optional_cupy.py

"""
This Gist illustrates how you can import cupy when it may or not be installed. Also works with frozen applications.

If cupy is not installed, or the CUDA_PATH system variable is not set, or the incorrect CUDA version is installed
(relevant for frozen applications), is_cupy_available = False.
"""

import warnings

is_cupy_available = False
try:
    # Try to import  cupy
    with warnings.catch_warnings():
        warnings.simplefilter("error")  # Raise warnings as UserWarning exception
        import cupy as cp  # type:ignore[import-untyped]
        import cupyx.scipy.fft as cpfft  # type:ignore[import-untyped]
except (ModuleNotFoundError, UserWarning):
    warnings.warn("CuPy is not installed, or you have not set the CUDA_PATH system variable.", stacklevel=2)
else:
    # Test cupy
    try:
        cp.fft.fft(cp.random.rand(128))
    except Exception as exc:
        warnings.warn("CuPy threw an exception during testing. Have you installed CUDA 12.3? "
                      f"Exception message:: {exc}", stacklevel=2)
    else:
        print("CuPy imported and tested OK.")
        is_cupy_available = True