[Python-Dev] PySequence_Check but no len (original) (raw)

Brett Cannon brett at python.org
Thu Jun 21 12:29:52 EDT 2018

Sorry, I don't quite follow.

On Thu, 21 Jun 2018 at 08:50 Christian Tismer <tismer at stackless.com> wrote:

Hi friends,

there is a case in the Python API where I am not sure what to do: If an object defines getitem() only but no len(), then PySequenceCheck() already is true and does not care.

Which matches https://docs.python.org/3/c-api/sequence.html#c.PySequence_Check .

From Objects/abstract.c:

int PySequence_Check(PyObject *s) { if (PyDict_Check(s)) return 0; return s != NULL && s->ob_type->tp_as_sequence && s->ob_type->tp_as_sequence->sq_item != NULL; }

So if I define no len, it simply fails. Is this intended?

What is "it" in this case that is failing? It isn't PySequence_Check() so I'm not sure what the issue is.

-Brett

I was mislead and thought this was the unlimited case, but it seems still to be true that sequences are always finite. Can someone please enlighten me? -- Christian Tismer-Sperling :^) tismer at stackless.com Software Consulting : http://www.stackless.com/ Karl-Liebknecht-Str. 121 : http://pyside.org 14482 Potsdam : GPG key -> 0xE7301150FB7BEE0E phone +49 173 24 18 776 <+49%20173%202418776> fax +49 (30) 700143-0023 <+49%2030%207001430023>

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