test_tix cannot import _default_root after test_idle

[vadmium]

BPO	27611
Nosy	@terryjreedy, @vadmium, @zware, @serhiy-storchaka
PRs	[Do Not Merge] Convert Misc/NEWS so that it is managed by towncrier #552
Files	tix_default_root.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 2016-09-25.14:45:24.220>
created_at = <Date 2016-07-25.02:07:16.743>
labels = ['type-bug', 'tests']
title = 'test_tix cannot import _default_root after test_idle'
updated_at = <Date 2017-03-31.16:36:37.012>
user = 'https://github.com/vadmium'

bugs.python.org fields:

activity = <Date 2017-03-31.16:36:37.012>
actor = 'dstufft'
assignee = 'none'
closed = True
closed_date = <Date 2016-09-25.14:45:24.220>
closer = 'serhiy.storchaka'
components = ['Tests']
creation = <Date 2016-07-25.02:07:16.743>
creator = 'martin.panter'
dependencies = []
files = ['43871']
hgrepos = []
issue_num = 27611
keywords = ['patch']
message_count = 14.0
messages = ['271206', '271219', '271220', '271221', '271225', '271226', '272822', '272823', '272839', '272844', '272846', '272860', '272862', '277376']
nosy_count = 5.0
nosy_names = ['terry.reedy', 'python-dev', 'martin.panter', 'zach.ware', 'serhiy.storchaka']
pr_nums = ['552']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue27611'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6']

[vadmium]

$ ./python -m unittest -v test.test_{idle,tix}
. . .
test_tix (unittest.loader._FailedTest) ... ERROR

======================================================================
ERROR: test_tix (unittest.loader._FailedTest)
----------------------------------------------------------------------

ImportError: Failed to import test module: test_tix
Traceback (most recent call last):
  File "/media/disk/home/proj/python/cpython/Lib/unittest/loader.py", line 153, in loadTestsFromName
    module = __import__(module_name)
  File "/media/disk/home/proj/python/cpython/Lib/test/test_tix.py", line 11, in <module>
    from tkinter import tix, TclError
  File "/media/disk/home/proj/python/cpython/Lib/tkinter/tix.py", line 30, in <module>
    from tkinter import _cnfmerge, _default_root
ImportError: cannot import name '_default_root'

Without test_idle, test_tix is skipped for me:

$ ./python -m unittest -v test.test_tix
test_tix_available (test.test_tix.TestTix) ... skipped 'Tix not available'

Reverting to before revision 064b29dde096 (bpo-24137) also fixes the failure.

[serhiy-storchaka]

There is a bug in tix. _default_root shouldn't be imported, since this is modifiable attribute.

[terryjreedy]

I could reverse the effect of test_idle calling tk.NoDefaultRoot by adding
tk._support_default_root = 1
tk._default_root = None
at the very end, but I take Serhiy's comment as suggesting that there should be no need.

[zware]

I think there are two bugs to be fixed here:

1. as Serhiy said, if tix needs _default_root, it should use it as tkinter._default_root instead of importing it directly

2. test_idle should not permanently modify the tkinter namespace

[python-dev]

New changeset 5c76f787e695 by Terry Jan Reedy in branch 'default':
Issue bpo-24137, issue bpo-27611: Restore tkinter after test_idle.
https://hg.python.org/cpython/rev/5c76f787e695

[terryjreedy]

bpo-24137 only patched default, so either too many versions were selected or there is another bug in test_tix. Martin and Serhiy can sort that out.

The restore patch I pushed is based on this from tkinter.__init__
-----

_support_default_root = 1
_default_root = None

def NoDefaultRoot():
    """Inhibit setting of default root window.

Call this function to inhibit that the first instance of
Tk is used for windows without an explicit parent window.
"""
global _support_default_root
_support_default_root = 0
global _default_root
_default_root = None
del _default_root

[python-dev]

New changeset a6a248479b66 by Terry Jan Reedy in branch 'default':
Issue bpo-27611, bpo-24137: Only change tkinter when easily restored.
https://hg.python.org/cpython/rev/a6a248479b66

[terryjreedy]

Ned Deily noticed the same problem when running with test.regrtest bpo-27714.

I cannot reproduce this issue when running both tests either with unittest or test.regrtest.

F:\Python\dev>36\pcbuild\win32\python_d.exe -m unittest test.test_tix test.test_idle test.test_tix
.............................................................................................................................................................................................................................
----------------------------------------------------------------------
Ran 221 tests in 3.959s

OK
F:\Python\dev>36\pcbuild\win32\python_d.exe -m test -ugui test_tix test_idle test_tix
Run tests sequentially
0:00:00 [1/3] test_tix
0:00:00 [2/3] test_idle
0:00:03 [3/3] test_tix
All 3 tests OK.
if __name__ == '__main__':
unittest.main(verbosity=2, exit=False)
+ tk._support_default_root = 1
+ tk._default_root = None

Zach, I don't know of any way to get either unittest or test.regrtest to run anything in test_idle after it runs the test collector *and* the tests. Do you?

The addition of tk.NoDefaultRoot() to both IDLE and its tests was suggested by Serhiy in bpo-24137. Doing so exposed several issues in htests but no real bugs in IDLE itself. My patch to restore tkinter module only works when test_idle is run as main. So as far as that patch goes, tkinter should only changed when the test is run as main. I will move the call. I have already changed my check script to run test_idle this way.

Otherwise, the easiest way to leave tkinter as it was when testing ends is to not change it. I am aware that tkinter tests avoid the by defining a mixin class with class methods that call and undo the call. It is used in 11 test classes within the tkinter and ttk tests. However, this refactoring would be harder to apply to IDLE tests and not sufficient in itself. It is at best a future project.

I added a guard to IDLE's NoDefaultRoot call for when pyshell.main is broken into multiple testable functions.

[python-dev]

New changeset cddd633b959f by Terry Jan Reedy in branch '2.7':
Issue bpo-27611: Don't import volatile attribute.
https://hg.python.org/cpython/rev/cddd633b959f

New changeset a42933335897 by Terry Jan Reedy in branch '3.5':
Issue bpo-27611: Don't import volatile attribute.
https://hg.python.org/cpython/rev/a42933335897

[serhiy-storchaka]

Terry, you committed not full patch. The tix module still doesn't work after NoDefaultRoot().