[Python-Dev] When val=b'', but val == b'' returns False (original) (raw)
[Python-Dev] When val=b'', but val == b'' returns False - bytes initialization
Antoine Pitrou solipsis at pitrou.net
Wed Dec 27 12:51:15 EST 2017
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On Wed, 27 Dec 2017 17:28:41 +0100 Antoine Pitrou <solipsis at pitrou.net> wrote:
On Wed, 27 Dec 2017 14:19:16 +0000 Jonathan Underwood <jonathan.underwood at gmail.com> wrote: > Hello, > > I am not sure if this is expected behaviour, or a bug. > > In a C extension module, if I create and return an empty bytes object like this: > > val = PyBytesFromStringAndSize (NULL, 20); > PySIZE(val) = 0;
I wouldn't call it "expected", but bytes objects are supposed to be NULL-terminated internally, so your code technically creates an invalid bytes object. The NULL-terminated constraint may be relied on by some code, for example when the string gets passed to a third-party C function.
Note this is really happening because you're allocating a 20-long bytes object and then shortening it to 0 bytes. PyBytes_FromStringAndSize() already stored a NULL byte in the 21st place.
Regards
Antoine.
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