New submission from Kevin Modzelewski:
(Using python 3 terminology) str_subtype_new is the function that creates
instances of any subtypes of bytes (ie is called by bytes_new if the requested
type is not PyBytes_Type -- looks like this function's name comes from python
2). Its approach is to create a bytes object using the same arguments, and
then copy the resulting data into the subclass-instance's memory. It does
tmp = bytes_new(&PyBytes_Type, args, kwds);
[error checking]
assert(PyBytes_CheckExact(tmp));
The problem is that bytes_new can return a subclass of bytes, if the argument
provides a __bytes__ method that returns a bytes-subtype. For example
class MyBytes(bytes):
pass
class C(object):
def __bytes__(self):
return MyBytes(b"hello world")
MyBytes(C()) # fails the assert
This doesn't seem to cause any issues other than the failing assert in debug
builds; it seems like the assert should just be relaxed from PyBytes_CheckExact
to PyBytes_Check since that's enough to guarantee that the upcoming
manipulation of the "tmp" variable is going to be valid. Also, this would
match how unicode_subtype_new behaves.
This bug also applies to Python 2, since I think the relevant code is the same,
though in that case it applies to str instead of bytes.
----------
components: Interpreter Core
messages: 247451
nosy: Kevin Modzelewski
priority: normal
severity: normal
status: open
title: Incorrect assert in str_subtype_new
versions: Python 2.7, Python 3.5
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue24731>
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