doctest assumes sys.displayhook hasn't been touched

[noam]

BPO	8048
Nosy	@birkenfeld, @florentx
Files	doctest.py.diff: Diff for doctest.py (from python 2.6) diff: Patch against Python 2, includes a test. better.patch: Better 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 2010-07-30.09:23:29.333>
created_at = <Date 2010-03-03.08:17:34.165>
labels = ['type-bug', 'library']
title = "doctest assumes sys.displayhook hasn't been touched"
updated_at = <Date 2010-07-30.09:23:29.332>
user = 'https://bugs.python.org/noam'

bugs.python.org fields:

activity = <Date 2010-07-30.09:23:29.332>
actor = 'georg.brandl'
assignee = 'none'
closed = True
closed_date = <Date 2010-07-30.09:23:29.333>
closer = 'georg.brandl'
components = ['Library (Lib)']
creation = <Date 2010-03-03.08:17:34.165>
creator = 'noam'
dependencies = []
files = ['16421', '16436', '16581']
hgrepos = []
issue_num = 8048
keywords = ['patch']
message_count = 4.0
messages = ['100334', '100423', '101312', '112054']
nosy_count = 3.0
nosy_names = ['georg.brandl', 'noam', 'flox']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'test needed'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue8048'
versions = ['Python 2.7', 'Python 3.2']

[noam]

Hello,

This bug is the cause of a bug reported about DreamPie: https://bugs.launchpad.net/bugs/530969

DreamPie (http://dreampie.sourceforge.net) changes sys.displayhook so that values will be sent to the parent process instead of being printed in stdout. This causes doctest to fail when run from DreamPie, because it implicitly assumes that sys.displayhook writes the values it gets to sys.stdout. This is why doctest replaces sys.stdout with its own file-like object, which is ready to receive the printed values.

The solution is simply to replace sys.displayhook with a function that will do the expected thing, just like sys.stdout is replaced. The patch I attach does exactly this.

Thanks,
Noam

[noam]

Ok, here's a patch (against current svn of Python 2) with a test case.

I had to fix three tests which combined pdb and doctest, since now, when run under doctest, pdb steps into the displayhook because it's a Python function and not a built-in function. The fix is just to return from the displayhook.

If you wish, I can prepare a patch for Python 3.

[noam]

Here is a better and much shorter patch: I use sys.__displayhook__ instead of implementing it in Python, which has the nice side effect of not changing pdb behaviour.

[birkenfeld]

Thanks, applied to 3k in r83268.