also, IMHO, we should open an issue named 'raise ValueError instead of OverflowError when a negative int is invalid', and leave for that
new issue some the changes (which you commented about in the PR).

I didn't want to open it without your approval.
here is what I thought should be the contents of the issue (feel
free to edit my draft as you wish and open the issue yourself,
if you think we should open it):


In various C functions, a negative int argument is invalid. in most of these
functions, ValueError is raised for a negative int, or at least for a small
negative int (i.e. a negative int that fits in some signed integer C
type).

as Serhiy mentioned in http://bugs.python.org/issue15988#msg289679 and in
code review comments in https://github.com/python/cpython/pull/668, it might
be that a ValueError should always be raised in such functions, upon receiving
a negative int (even upon receiving a big negative int, such as (-1 << 1000)).

the following functions were identified as relevant only while working on
#15988, so there are probably (a lot?) more relevant functions.

functions where OverflowError is raised only for big negative ints:
    - Objects/bytesobject.c - bytes_new
    - Objects/bytearrayobject.c - bytearray_init
    - functions that would be fixed as part of #29819?
        * Modules/_io/stringio.c - _io_StringIO_truncate_impl
        * Modules/_io/bytesio.c - _io_BytesIO_truncate_impl

functions where OverflowError is raised for any negative int (so a change would
probably break some users code):
    - Objects/longobject.c:
        * PyLong_AsUnsignedLong
        * PyLong_AsSize_t
    - Modules/_ctypes/_ctypes.c - PyCArrayType_new


Note: while patching these functions, one should also make sure that the
patched functions produce consistent error messages, as explained in #15988
(in which it was decided to leave these functions (which currently produce
inconsistent error messages) to this issue.)