Don't print traceback header if traceback is None in TracebackException

[Drekin]

BPO	24695
Nosy	@rhettinger, @rbtcollins, @berkerpeksag, @iritkatriel
Files	issue24695.diff

^{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 2015-07-24.14:39:03.743>
created_at = <Date 2015-07-23.14:42:19.577>
labels = ['type-bug', 'library']
title = "Don't print traceback header if traceback is None in TracebackException"
updated_at = <Date 2020-11-27.10:14:41.256>
user = 'https://bugs.python.org/Drekin'

bugs.python.org fields:

activity = <Date 2020-11-27.10:14:41.256>
actor = 'iritkatriel'
assignee = 'none'
closed = True
closed_date = <Date 2015-07-24.14:39:03.743>
closer = 'berker.peksag'
components = ['Library (Lib)']
creation = <Date 2015-07-23.14:42:19.577>
creator = 'Drekin'
dependencies = []
files = ['40001']
hgrepos = []
issue_num = 24695
keywords = ['patch']
message_count = 13.0
messages = ['247208', '247220', '247231', '247241', '247277', '247278', '247279', '247434', '247436', '247437', '247441', '247443', '381939']
nosy_count = 6.0
nosy_names = ['rhettinger', 'rbcollins', 'python-dev', 'berker.peksag', 'Drekin', 'iritkatriel']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue24695'
versions = ['Python 3.5', 'Python 3.6']

[Drekin]

The documentation of traceback.print_exception says "if traceback is not None, it prints a header Traceback (most recent call last):". That also meant that the header wasn't printed if traceback was None. However, the new Python 3.5 TracebackException object always prints the header.

[rbtcollins]

Huh,indeed.

So clearly we should have a test for that behaviour (and fix it).

We're very close to the 3.5 release date, but this is a regression - care to whip up a patch?

[berkerpeksag]

Here is a patch. I was pretty sure that I've already created an issue for this but couldn't find it now.

[rhettinger]

This patch looks correct, applies cleanly, and passes tests.

[python-dev]

New changeset b45077269aaa by Berker Peksag in branch '3.5':
Issue bpo-24695: Fix a regression in traceback.print_exception()
https://hg.python.org/cpython/rev/b45077269aaa

New changeset 2825c87d3f72 by Berker Peksag in branch 'default':
Issue bpo-24695: Fix a regression in traceback.print_exception()
https://hg.python.org/cpython/rev/2825c87d3f72

[berkerpeksag]

Fixed in 3.5 and default branches. Thank you for your review, Raymond.

[Drekin]

Thank you all for a quick reaction.

[Drekin]

Just out of my curiosity – why is not this issue listed in Python 3.5b4 changelog even though the issue is fixed there?

[berkerpeksag]

Could you please share the link of the changelog you've mentioned? Unless I'm missing something, this issue is already listed in the changelog: https://hg.python.org/releasing/3.5/file/f65605b99cb4/Misc/NEWS#l37

[Drekin]

I meant this one: https://docs.python.org/3.5/whatsnew/changelog.html#python-3-5-beta-4 .

[berkerpeksag]

Looks like a cache issue. I've just fixed it: https://docs.python.org/3.5/whatsnew/changelog.html