[New-bugs-announce] [issue28214] Improve exception reporting for problematic __set_name__ attributes

[Tim Graham]

New submission from Tim Graham:

As requested by Nick [0], this is a usability issue against CPython 3.6 to provide a better chained TypeError in this case:

class _TokenType(tuple):
    parent = None

    def __getattr__(self, name):
        new = _TokenType(self + (name,))
        setattr(self, name, new)
        new.parent = self
        return new

Token = _TokenType()

Keyword = Token.Keyword

class KeywordCaseFilter(object):
    ttype = Keyword


Traceback (most recent call last):
  File "test.py", line 14, in <module>
    class KeywordCaseFilter(object):
TypeError: '_TokenType' object is not callable

The exception should report the specific object with the problematic __set_name__ attribute (rather than just passing along the underlying exception), as well as supporting __set_name__ = None to explicitly disable further lookup processing.

Follow up to #27366.

[0] https://github.com/andialbrecht/sqlparse/issues/286#issuecomment-248208900

----------
components: Interpreter Core
messages: 277027
nosy: Tim.Graham, ncoghlan
priority: normal
severity: normal
status: open
title: Improve exception reporting for problematic __set_name__ attributes
type: behavior
versions: Python 3.6, Python 3.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28214>
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