`CatalogExt.has()` throws KeyError on unknown extension
Closed this issue · 8 comments
import pystac
c = pystac.Collection(id="foo", description="bar", extent=None)
c.ext.has("meh")throws
KeyError: "Extension 'meh' is not a valid extension. Options are ['classification', 'cube', 'eo', 'file', 'grid', 'item_assets', 'mgrs', 'pc', 'proj', 'raster', 'sar', 'sat', 'sci', 'storage', 'table', 'timestamps', 'version', 'view', 'xarray']"
Is it the intended design to raise an exception here?
As a user, I expect has() to return false if the specified extension is not available for consumption.
I think that behavior is intentional but open to suggestions on how it could be improved. That error is meant to say: there is no extension named "meh" this is as opposed to the False condition which would indicate that the extension in question has not been added to the specified collection.
To give some context about my expected behavior:
As a user or even more strongly as a library developer I want to build on pystac and write something like
if collection.ext.has("foo"):
# do something with "foo" extension related metadataWithout worrying about whether/how "foo" is defined as an extension in some other place.
Now I have to wrap that in try-catch boilerplate
Or is there a cleaner way to first dynamically check if the "foo" extension exists?
Something like
if pystac.ext.has("foo") and collection.ext.has("foo"):
# ...But then again, from user standpoint this looks a bit redundant and boilerplaty
We don't currently have a graceful mechanism to register third party extensions into the ext attribute of catalog/collection/item/asset, so pystac.extensions.ext.EXTENSION_NAMES list is the exhaustive list of supported extensions — unless you're doing something wild, that list should be fixed for your current pystac version.
Or is there a cleaner way to first dynamically check if the "foo" extension exists?
Yup:
from pystac.extensions.ext import EXTENSION_NAMES
if "foo" in EXTENSION_NAMES and collection.ext.has("foo"):
...EXTENSION_NAMES is apparently a typing.Literal object, and on Python 3.9 (which we still want to support) that does not work:
from pystac.extensions.ext import EXTENSION_NAMES
"foo" in EXTENSION_NAMESgives
TypeError: Parameters to generic types must be types. Got 0.
(It only seems to work on python 3.11 or higher)
Ah gotcha ... For <= 3.10 you could probably do this instead:
from pystac.extensions.ext import EXTENSION_NAMES_MAPPING
"foo" in EXTENSION_NAMES_MAPPINGI am fine with changing the behavior of has if that makes more sense. Do you think that has is clearer than just using hasattr though?
if hasattr(c.ext, "meh"):
...I am fine with changing the behavior of has if that makes more sense.
I don't think it does — IMO "does this thing implement this known extension" needs a different behavior than "we don't know what that extension is".