[issue15573] Support unknown formats in memoryview comparisons

[STINNER Victor]

STINNER Victor added the comment:

Can't we start with something simple (for ptyhon 3.3?), and elaborate
later? In my specific example, both object have the same format string and
the same content. So i expect that they are equal.
Le 10 août 2012 19:47, "Martin v. Löwis" <report at bugs.python.org> a écrit :

>
> Martin v. Löwis added the comment:
>
> > So v.format must equal w.format, where format is a format string in
> > struct module syntax. The topic of this issue is to determine under
> > what circumstances two strings in struct module syntax are considered
> > equal.
>
> And that is exactly my question: We don't need a patch implementing
> it (yet), but a specification of what is to be implemented first.
>
> I know when two strings are equal (regardless of their syntax):
> if they have the same length, and contain the same characters in
> the same order. Apparently, you have a different notion of "equal"
> for strings in mind, please be explicitly what that notion is.
>
> > memoryview can compare against any object with a getbufferproc, in this
> > case array.array. memoryview_richcompare() calls
> PyObject_GetBuffer(other)
> > and proceeds to compare its own internal Py_buffer v against the obtained
> > Py_buffer w.
>
> Can this be expressed on Python level as well? I.e. is it correct
> to say: an array/buffer/memoryview A is equal to an object O iff
> A is equal to memoryview(O)? Or could it be that these two equivalences
> might reasonably differ?
>
> > Hence my proposal to demand a strict canonical form for PEP-3118 format
> > strings, which would be a proper subset of struct module format strings.
>
> Can you kindly phrase this as a specification? Who is demanding what
> from whom?
>
> Proposal: two format strings are equal if their canonical forms
> are equal strings. The canonical form C of a string S is created by ???
>
> However, it appears that you may have something different in mind
> where things are rejected/fail to work if the canonical form isn't
> originally provided by somebody (whom?)
>
> So another Proposal: two format strings are equal iff they are
> in both in canonical form and are equal strings.
>
> This would imply that a format string which is not in canonical
> form is not equal to any other strings, not even to itself, so
> this may still not be what you want. But I can't guess what it
> is that you want.
>
> ----------
>
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> Python tracker <report at bugs.python.org>
> <http://bugs.python.org/issue15573>
> _______________________________________
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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue15573>
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