Minor UX improvement: Custom error for missing codec.

[cwognum]

I want to preface this by saying that this would be a minor UX improvement. Not blocking at all!

Context

Zarr is extensible with custom codecs, e.g. imagecodecs. Naturally, this can lead to situations where the environment in which a Zarr archive was written is not the same as the environment in which a Zarr archive is read. This can lead to missing codecs when trying to load data from a Zarr archive.

Description

If you try to access a Zarr array that uses a codec which is not registered locally, a generic ValueError is thrown.

ValueError: codec not available: 'imagecodecs_jpeg2k'

In downstream libraries that use Zarr under the hood, this makes it harder to catch this specific error and to suggest an appropriate solution.

Instead, it would be great if a custom error is thrown that holds some additional information. For example

class InvalidCodecError(Exception):
    """Raised when an expected codec is not registered."""

    def __init__(self, codec_name: str):
        self.codec_name = codec_name
        super().__init__(f"Codec not available: '{codec_name}'")

This would enable something like:

try: 
    arr = root["array"]
except InvalidCodecError as error:
    if error.codec_name == "imagecodecs_jpeg2k":
        raise RuntimeError("This Zarr archive requires `imagecodecs`, to install it use ...") from error

[dstansby]

👍 this sounds like a great idea - would you be able to open a PR to add this?