Broken compatibility in FrameSummary equality

[serhiy-storchaka]

BPO	25111
Nosy	@vstinner, @rbtcollins, @berkerpeksag, @serhiy-storchaka
Files	traceback_FrameSummary_equality.patch traceback_FrameSummary_equality_2.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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2015-09-29.19:37:09.222>
created_at = <Date 2015-09-14.17:48:43.752>
labels = ['type-bug', 'library']
title = 'Broken compatibility in FrameSummary equality'
updated_at = <Date 2015-09-29.19:37:09.221>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2015-09-29.19:37:09.221>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2015-09-29.19:37:09.222>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2015-09-14.17:48:43.752>
creator = 'serhiy.storchaka'
dependencies = []
files = ['40463', '40500']
hgrepos = []
issue_num = 25111
keywords = ['patch']
message_count = 7.0
messages = ['250693', '250953', '251722', '251760', '251834', '251835', '251880']
nosy_count = 5.0
nosy_names = ['vstinner', 'rbcollins', 'python-dev', 'berker.peksag', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue25111'
versions = ['Python 3.5', 'Python 3.6']

[serhiy-storchaka]

Since 3.5 traceback.extract_tb() and traceback.extract_stack() return a list (actually list's subclass StackSummary) of FrameSummary objects instead of a list of tuples. FrameSummary is not fully compatible with tuple. One important incompatibility is in the comparing.

>>> import traceback
>>> traceback.extract_stack()[0] == ('<stdin>', 1, '<module>', '')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/serhiy/py/cpython-3.5/Lib/traceback.py", line 254, in __eq__
    return (self.filename == other.filename and
AttributeError: 'tuple' object has no attribute 'filename'

In general __eq__ shouldn't raise an exception. bpo-25108 is needed to be fixed first for tests.

Here is a patch that restores compatibility.

An alternative solution would be to make FrameSummary a subclass of tuple (namedtuple).

[serhiy-storchaka]

Fixed patch and added tests.

[serhiy-storchaka]

Ping.

[berkerpeksag]

LGTM

+ self.assertEqual(f, tuple(f))
+ self.assertEqual(tuple(f), f)

It would be good to add a comment to explain why we test both variants, but it's not really important.

[vstinner]

traceback_FrameSummary_equality_2.patch looks good to me, but I have the same remark than Berker (see the review).

[rbtcollins]

LGTM too.

[python-dev]

New changeset 2ecb7d4d9e0b by Serhiy Storchaka in branch '3.5':
Issue bpo-25111: Fixed comparison of traceback.FrameSummary.
https://hg.python.org/cpython/rev/2ecb7d4d9e0b

New changeset f043182a81d7 by Serhiy Storchaka in branch 'default':
Issue bpo-25111: Fixed comparison of traceback.FrameSummary.
https://hg.python.org/cpython/rev/f043182a81d7