Make cattrs and cattr.errors namespaces contain all error types from cattrs.errors

[jap]

Without this, trying to do something along the lines of

import cattr.errors

try:
  ...
except cattr.errors.BaseValidationError as exc:
  ...

fails miserably because it was only importing StructureHandlerNotFoundError from cattrs.errors

Besides that, importing cattrs (with s) causes cattrs.errors to be imported from cattr.errors which then causes the same problem.

import cattrs.errors also has this issue but Python's import machinery is too complicated for me to understand or explain why.

The only way to get a reachable BaseValidationError is by doing

from cattrs.errors import BaseValidationError

which would cause code review remarks during the day job where we're trying to get rid of "from-imports".

[Tinche]

Hi,

cattr is kind of a deprecated namespace, it's not going away but new stuff is only going to be added to cattrs to gently encourage migration. I have very recently moved the actual errors to cattrs.errors, so my first question would be if the main branch still has the problem you're experiencing?

[jap]

It is, with your main branch checked out:

lil-bob:cattrs spaans$ pip install --editable .
Obtaining file:///Users/spaans/src/cattrs
  Installing build dependencies ... done
  Checking if build backend supports build_editable ... done
  Getting requirements to build editable ... done
  Preparing editable metadata (pyproject.toml) ... done
Collecting exceptiongroup
  Using cached exceptiongroup-1.0.0rc2-py3-none-any.whl (10 kB)
Collecting attrs>=20
  Using cached attrs-21.4.0-py2.py3-none-any.whl (60 kB)
Building wheels for collected packages: cattrs
  Building editable for cattrs (pyproject.toml) ... done
  Created wheel for cattrs: filename=cattrs-22.2.0.dev0-py3-none-any.whl size=4915 sha256=f4138de6c395a84340443b1d66191eb3fba37cc1e6032639ae4580eeefb5ac6a
  Stored in directory: /private/var/folders/hs/y6mmqk9d4p97tr05d11crdb80000gn/T/pip-ephem-wheel-cache-grv9nq2h/wheels/cb/07/86/7e063245dba45861348d66e20e3ff2da1b3ebd669531de559d
Successfully built cattrs
Installing collected packages: exceptiongroup, attrs, cattrs
Successfully installed attrs-21.4.0 cattrs-22.2.0.dev0 exceptiongroup-1.0.0rc2
lil-bob:cattrs spaans$ python3
Python 3.10.3 (main, Mar 29 2022, 22:28:06) [Clang 13.1.6 (clang-1316.0.21.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import cattrs.errors
>>> dir(cattrs.errors)
['StructureHandlerNotFoundError', '__all__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__']

[jap]

and with my branch:

lil-bob:cattrs spaans$ git checkout origin/error-import 
Previous HEAD position was 9e740a8 Tweak test
HEAD is now at 079b6f7 Ensure all error types are reachable through module imports
lil-bob:cattrs spaans$ python3
Python 3.10.3 (main, Mar 29 2022, 22:28:06) [Clang 13.1.6 (clang-1316.0.21.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import cattr.errors
>>> dir(cattrs.errors)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'cattrs' is not defined
>>> import cattrs.errors
>>> dir(cattrs.errors)
['BaseValidationError', 'ClassValidationError', 'ForbiddenExtraKeysError', 'IterableValidationError', 'StructureHandlerNotFoundError', '__all__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__']

[jap]

I think the from cattr import ..., errors, ... in cattrs.__init__ is to blame, so it may be easier to fix by just letting that import from its own errors module, but then there still is the issue that cattr.errors only imports one class instead of all for people using the legacy namespace.

[jap]

I put an additional commit in https://github.com/jap/cattrs/tree/error-import2 which takes the above into account, and actually exposes the errors on the cattrs namespace directly, as implied by https://cattrs.readthedocs.io/en/latest/validation.html (which refers to cattrs.ClassValidationError for example, which currently really doesn't exist.)

[Tinche]

Sorry, I might have posted my reply too early. Can you try with 792a5f4?

This is what I'm seeing:

$ python -c "import cattrs.errors; print(dir(cattrs.errors))"
['BaseValidationError', 'ClassValidationError', 'ExceptionGroup', 'ForbiddenExtraKeysError', 'IterableValidationError', 'Optional', 'Set', 'StructureHandlerNotFoundError', 'Type', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__']

[codecov-commenter]

Codecov Report

Merging #252 (be42812) into main (38205da) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head be42812 differs from pull request most recent head e379bce. Consider uploading reports for the commit e379bce to get more accurate results

@@           Coverage Diff           @@
##             main     #252   +/-   ##
=======================================
  Coverage   97.01%   97.01%           
=======================================
  Files          16       16           
  Lines        1339     1340    +1     
=======================================
+ Hits         1299     1300    +1     
  Misses         40       40           

Impacted Files	Coverage Δ
src/cattrs/__init__.py	100.00% <100.00%> (ø)

📣 Codecov can now indicate which changes are the most critical in Pull Requests. Learn more

[jap]

Confirmed - your latest version fixes the original issue for me.
Note that the cattr.errors namespace is still like it was before, but maybe that is not an issue given that it is deprecated; however, cattrs itself doesn't contain the error classes like the validation page implies.

[Tinche]

Agreed, would be great if you could open a new PR (or repurpose this one) to just re-export the exceptions from cattrs.__init__ ;)

[jap]

I'll make some time for that this week!

[jap]

Rebased against your main branch and made things work.

[Tinche]

Sorry, I forgot about this for a while. Can you add a small HISTORY entry and I can merge?

[jap]

Sure, done!

[Tinche]

Thanks, I merged this into main manually manually!