Make TOMLDecodeError show 'tomli' as its module

[goodmami]

The README and tests show tomli.TOMLDecodeError as the error class to catch, which I take to mean it is the public API, but what's printed is tomli._parser.TOMLDecodeError because that's the module it's defined in:

>>> import tomli
>>> tomli.loads('[foo')
Traceback (most recent call last):
  ...
tomli._parser.TOMLDecodeError: Expected "]" at the end of a table declaration (at end of document)

This PR tells the exception class to use 'tomli' as its module so the displayed exception matches the public API:

>>> tomli.loads('[foo')
Traceback (most recent call last):
  ...
tomli.TOMLDecodeError: Expected "]" at the end of a table declaration (at end of document)

The exception is still defined in its original location, so if anyone saw the original error message and tried to catch the exception from toml._parser, it would still work:

>>> tomli.TOMLDecodeError is tomli._parser.TOMLDecodeError
True
>>> try:
...     tomli.loads('[foo')
... except tomli._parser.TOMLDecodeError:
...     print('still good')
... 
still good

[codecov-commenter]

Codecov Report

Merging #135 (e94ea77) into master (8917fe3) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #135   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines          494       495    +1     
  Branches        93        93           
=========================================
+ Hits           494       495    +1     

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

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[goodmami]

It looks like the failed builds are a pytest bug on Python 3.11 (pytest-dev/pytest#9181). #133 and #134 show the same error message.

[hukkin]

Thanks for the PR!

I think I'd slightly prefer having this done in __init__.py in the same way (and with the same comment) that the standard library does here, as I find this more part of the import path manipulation happening in __init__ rather than implementation of the class defined in _parser.py. Would you mind doing that change?

It'd also be great to have a small test that fails without this line. Just a simple assert tomli.TOMLDecodeError.__module__ == "tomli" perhaps, in test_error.py.

[goodmami]

I find this more part of the import path manipulation happening in __init__ rather than implementation of the class

Good point. I agree.

It'd also be great to have a small test that fails without this line.

Done. I tested that it fails without the change and passes with it.

[hukkin]

This is great, thanks a lot!