Initially hasattr() suppressed all raised exceptions. In issue2196 hasattr() was changed to suppress only Exception exceptions and propagate exceptions like SystemExit and KeyboardInterrupt. In issue9666 hasattr() was changed to suppress only AttributeError.

But C API functions, PyObject_HasAttr() and like, were not changed. PyObject_HasAttr() is documented as an equivalent of hasattr(), but there is undocumented difference. The C code that uses PyObject_HasAttr() starves from the same problem as the Python code that used old hasattr().

The only solution of this problem is getting rid of PyObject_HasAttr() if favor of PyObject_GetAttr(). In this issue I'm going to propose a set of PRs that replace PyObject_HasAttr() invocations in different components with more correct code.

New changeset 04e36af9b88cd5e80fc818e51d46f07252a2ff3f by Serhiy Storchaka in branch 'master':
bpo-31572: Get rid of using _PyObject_HasAttrId() in pickle. (#3729)
https://github.com/python/cpython/commit/04e36af9b88cd5e80fc818e51d46f07252a2ff3f

> The only solution of this problem is getting rid of PyObject_HasAttr() if favor of PyObject_GetAttr().

I don't understand why.  Why not fix PyObject_HasAttr() like hasattr() was?

hasattr() can return True, False, or raise an exception. But PyObject_HasAttr() just returns an integer: 0 for False, not 0 for True. There is no way to return an error, and existing code doesn't expect that PyObject_HasAttr() returns an error. Leaking an exception from PyObject_HasAttr() will break existing code.

New changeset 77af0a3bcab666a356eea2927a8031a7578d60d2 by Serhiy Storchaka in branch '3.6':
[3.6] bpo-31572: Get rid of using _PyObject_HasAttrId() in pickle. (GH-3729). (#4081)
https://github.com/python/cpython/commit/77af0a3bcab666a356eea2927a8031a7578d60d2

New changeset d4f8480dfe89447587550a85b61d4e9faf827e98 by Serhiy Storchaka in branch 'master':
bpo-31572: Don't silence unexpected errors in the _warnings module. (#3731)
https://github.com/python/cpython/commit/d4f8480dfe89447587550a85b61d4e9faf827e98

New changeset 1707e4020fa8dca8e6a3ac4f9da105b54d597b66 by Serhiy Storchaka in branch 'master':
bpo-31572: Silence only AttributeError when get the __copy__ attribute in itertools.tee(). (#3724)
https://github.com/python/cpython/commit/1707e4020fa8dca8e6a3ac4f9da105b54d597b66

New changeset 60c3d3551a96febac7b6016fb44605643842c686 by Serhiy Storchaka in branch 'master':
bpo-31572: Get rid of _PyObject_HasAttrId() in dict and OrderedDict. (#3728)
https://github.com/python/cpython/commit/60c3d3551a96febac7b6016fb44605643842c686

New changeset bba2239c17a404fc99524bfbf8126c9b3b7fb343 by Serhiy Storchaka in branch 'master':
bpo-31572: Get rid of _PyObject_HasAttrId() in the ASDL parser. (#3725)
https://github.com/python/cpython/commit/bba2239c17a404fc99524bfbf8126c9b3b7fb343

New changeset 4d9aec022063dcfc4cf40ae46b1c4a968297e664 by Serhiy Storchaka in branch 'master':
bpo-31572: Get rid of PyObject_HasAttr() and _PyObject_HasAttrId() in the _io module. (#3726)
https://github.com/python/cpython/commit/4d9aec022063dcfc4cf40ae46b1c4a968297e664

It seems like this issue caused a regression in _warnings: please see bpo-33509.

New changeset 398bd27967690f2c1a8cbf8d47a5613edd9cfb2a by Serhiy Storchaka in branch 'master':
bpo-32787: Better error handling in ctypes. (#3727)
https://github.com/python/cpython/commit/398bd27967690f2c1a8cbf8d47a5613edd9cfb2a