Don't show astroid.DuplicateBasesError for attribute access

[cdce8p]

Steps

• Add yourself to CONTRIBUTORS if you are a new contributor.
• Add a ChangeLog entry describing what your PR does.
• If it's a new feature or an important bug fix, add a What's New entry in
  doc/whatsnew/<current release.rst>.
• Write a good description on what the PR does.

Description

Previously an attribute access to a class which has duplicate bases would result in an astroid.DuplicateBasesError.
Note: The error for duplicate-bases was / is still printed.

Without MR

************* Module functional.d.duplicate_bases
tests/functional/d/duplicate_bases.py:5:0: E0241: Duplicate bases for class 'Duplicates' (duplicate-bases)
Traceback (most recent call last):
  File "/Users/.../pylint/venv-39_link/bin/pylint", line 33, in <module>
    sys.exit(load_entry_point('pylint', 'console_scripts', 'pylint')())
  File "/Users/.../pylint/pylint/__init__.py", line 24, in run_pylint
    PylintRun(sys.argv[1:])
  File "/Users/.../pylint/pylint/lint/run.py", line 358, in __init__
    linter.check(args)
  File "/Users/.../pylint/pylint/lint/pylinter.py", line 877, in check
    self._check_files(
  File "/Users/.../pylint/pylint/lint/pylinter.py", line 911, in _check_files
    self._check_file(get_ast, check_astroid_module, name, filepath, modname)
  File "/Users/.../pylint/pylint/lint/pylinter.py", line 937, in _check_file
    check_astroid_module(ast_node)
  File "/Users/.../pylint/pylint/lint/pylinter.py", line 1071, in check_astroid_module
    retval = self._check_astroid_module(
  File "/Users/.../pylint/pylint/lint/pylinter.py", line 1116, in _check_astroid_module
    walker.walk(ast_node)
  File "/Users/.../pylint/pylint/utils/ast_walker.py", line 75, in walk
    self.walk(child)
  File "/Users/.../pylint/pylint/utils/ast_walker.py", line 75, in walk
    self.walk(child)
  File "/Users/.../pylint/pylint/utils/ast_walker.py", line 75, in walk
    self.walk(child)
  File "/Users/.../pylint/pylint/utils/ast_walker.py", line 72, in walk
    callback(astroid)
  File "/Users/.../pylint/pylint/checkers/typecheck.py", line 981, in visit_attribute
    for n in owner.getattr(node.attrname)
  File "/Users/.../astroid/astroid/scoped_nodes.py", line 2444, in getattr
    result = [self.special_attributes.lookup(name)]
  File "/Users/.../astroid/astroid/interpreter/objectmodel.py", line 124, in lookup
    return getattr(self, IMPL_PREFIX + name)
  File "/Users/.../astroid/astroid/interpreter/objectmodel.py", line 426, in attr___mro__
    mro = self._instance.mro()
  File "/Users/.../astroid/astroid/scoped_nodes.py", line 2937, in mro
    return self._compute_mro(context=context)
  File "/Users/.../astroid/astroid/scoped_nodes.py", line 2926, in _compute_mro
    unmerged_mro = list(clean_duplicates_mro(unmerged_mro, self, context))
  File "/Users/.../astroid/astroid/scoped_nodes.py", line 113, in clean_duplicates_mro
    raise exceptions.DuplicateBasesError(
astroid.exceptions.DuplicateBasesError: Duplicates found in MROs (Duplicates), (str, object), (str, object), (str, str) for <ClassDef.Duplicates l.5 at 0x7fb0c698ffa0>.

With

************* Module functional.d.duplicate_bases
tests/functional/d/duplicate_bases.py:5:0: E0241: Duplicate bases for class 'Duplicates' (duplicate-bases)

Type of Changes

	Type
✓	🐛 Bug fix

[coveralls]

Coverage increased (+0.001%) to 91.61% when pulling 58390aa on cdce8p:fix-duplicate-bases-error into 8b18d91 on PyCQA:master.

[Pierre-Sassoulas]

Nice fix ! Strange that no one opened an issue for this ? I added a suggestion but feel free to merge.

[Pierre-Sassoulas]

Suggested change

	except astroid.DuplicateBasesError:
	except astroid.DuplicateBasesError:
	# See https://github.com/PyCQA/pylint/pull/4317

[cdce8p]

I'm not sure this is worth it. For one, you can get this information via git blame. Additionally the added test will catch if it's missing.