assertion error in complex division

[pitrou]

BPO	22604
Nosy	@malemburg, @mdickinson, @pitrou, @vstinner, @ericvsmith, @ezio-melotti, @serhiy-storchaka
Files	c_quot_nan.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2014-10-10.23:20:21.243>
created_at = <Date 2014-10-10.15:35:13.117>
labels = ['interpreter-core', 'type-bug']
title = 'assertion error in complex division'
updated_at = <Date 2014-10-10.23:20:21.241>
user = 'https://github.com/pitrou'

bugs.python.org fields:

activity = <Date 2014-10-10.23:20:21.241>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2014-10-10.23:20:21.243>
closer = 'pitrou'
components = ['Interpreter Core']
creation = <Date 2014-10-10.15:35:13.117>
creator = 'pitrou'
dependencies = []
files = ['36869']
hgrepos = []
issue_num = 22604
keywords = ['patch']
message_count = 7.0
messages = ['229011', '229016', '229019', '229025', '229041', '229042', '229043']
nosy_count = 9.0
nosy_names = ['lemburg', 'mark.dickinson', 'pitrou', 'vstinner', 'eric.smith', 'stutzbach', 'ezio.melotti', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue22604'
versions = ['Python 2.7', 'Python 3.4', 'Python 3.5']

[pitrou]

This only happens in debug mode:

>>> complex(0.0, 0.0) / complex(float('nan'), 0.0)
python: Objects/complexobject.c:98: _Py_c_quot: Assertion `b.imag != 0.0' failed.

In release mode, this gives:

>>> complex(0.0, 0.0) / complex(float('nan'), 0.0)
(nan+nanj)

(is it the right result?)

[serhiy-storchaka]

I think it is the right result.

>>> 0.0 / float('nan')
nan

[pitrou]

Here is a patch.

[mdickinson]

Patch LGTM.

(is it the right result?)

Difficult to tell :-). Complex arithmetic in general isn't well standardised. Annex G of the C standard is about as close I've seen. But it doesn't look terribly wrong.

[python-dev]

New changeset 0c8f45caf697 by Antoine Pitrou in branch '3.4':
Issue bpo-22604: Fix assertion error in debug mode when dividing a complex number by (nan+0j).
https://hg.python.org/cpython/rev/0c8f45caf697

New changeset af0104aed5b1 by Antoine Pitrou in branch 'default':
Issue bpo-22604: Fix assertion error in debug mode when dividing a complex number by (nan+0j).
https://hg.python.org/cpython/rev/af0104aed5b1

New changeset cd4ecaf38283 by Antoine Pitrou in branch '2.7':
Issue bpo-22604: Fix assertion error in debug mode when dividing a complex number by (nan+0j).
https://hg.python.org/cpython/rev/cd4ecaf38283

[pitrou]

Ok, I've committed the patch. Let's just see if the buildbots behave.

[pitrou]

They seem to have behaved! Congratulations, buildbots!