Raise subclass of AttributeError in __getattr__

[lilyminium]

Fixes #986

• Tag issue being addressed
• Add tests
• Update docstrings/documentation, if applicable
• Lint codebase
• Update changelog

[codecov]

Codecov Report

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Report is 84 commits behind head on master.

Additional details and impacted files

[mattwthompson]

I was pretty confused my some of the behavior of these attributes but then I realized they used the descriptor pattern, which has tripped me up in the past. Looks like it does what you wanted in the bug report:

>>> from openff.toolkit.typing.engines.smirnoff import ForceField
/Users/mwt/software/openforcefield/openff/toolkit/utils/exceptions.py:18: DeprecationWarning: ParseError is DEPRECATED and will be removed in a future release of the OpenFF Toolkit.
  warnings.warn(warning_msg, DeprecationWarning)
>>> ff = ForceField('openff_unconstrained-1.3.0.offxml')
>>> lc = ff.get_parameter_handler("LibraryCharges")
>>> hasattr(lc.parameters[0], "charge1")
True
>>> hasattr(lc.parameters[0], "charge2")
False
>>> hasattr(lc.parameters[0], "charge100")
False
>>> getattr(lc.parameters[0], "charge2")
Traceback (most recent call last):
  File "/Users/mwt/software/openforcefield/openff/toolkit/typing/engines/smirnoff/parameters.py", line 1105, in __getattr__
    return indexed_attr_value[index]
  File "/Users/mwt/software/openforcefield/openff/toolkit/utils/collections.py", line 119, in __getitem__
    return super().__getitem__(item)
IndexError: list index out of range

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mwt/software/openforcefield/openff/toolkit/typing/engines/smirnoff/parameters.py", line 1107, in __getattr__
    raise MissingIndexedAttributeError(
openff.toolkit.utils.exceptions.MissingIndexedAttributeError: 'charge2' is out of bounds for indexed attribute 'charge'
>>> getattr(lc.parameters[0], "charge1")
Quantity(value=1.0, unit=elementary charge)
>>> getattr(lc.parameters[0], "charge100")
Traceback (most recent call last):
  File "/Users/mwt/software/openforcefield/openff/toolkit/typing/engines/smirnoff/parameters.py", line 1105, in __getattr__
    return indexed_attr_value[index]
  File "/Users/mwt/software/openforcefield/openff/toolkit/utils/collections.py", line 119, in __getitem__
    return super().__getitem__(item)
IndexError: list index out of range

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mwt/software/openforcefield/openff/toolkit/typing/engines/smirnoff/parameters.py", line 1107, in __getattr__
    raise MissingIndexedAttributeError(
openff.toolkit.utils.exceptions.MissingIndexedAttributeError: 'charge100' is out of bounds for indexed attribute 'charge'

[mattwthompson]

Non-blocking: We should plan to remove the inheritance from IndexError and KeyError at some point but I haven't thought about how to communicate/implement this. I wouldn't want a message warning users to not catch as IndexError/KeyError if they're not doing that, or even close to that specific case. If it's not tractable it's probably okay to just leave the other errors in long-term.

[j-wags]

Any blockers to merging? This should be good to go once releasenotes are updated.

[lilyminium]

Any blockers to merging?

@j-wags not that I know of