After partial first review:

Squeezer only applies to Shell, not editor or output windows. So it seems that ii should only be imported into pyshell and the handler only bound in PyShell. This itself could be fixed in another issue. However, some of the existing and proposed code

The Squeezer.init check "if isinstance(editwin, PyShell):" seems unneeded as the event handler function can only be called from the Shell write() and context menu.

The statement "Tab width is configurable" in Squeezer.count_lines is not true in IDLE and especially not in Shell. Configdialog lines 8 and 9, written in 2003 and 2005, say
"Note that tab width in IDLE is currently fixed at eight due to Tk issues.
Refer to comments in EditorWindow autoindent code for details."
I did not find anything about Tk issues in the autoindent code following editor line 1208. The comment may be obsolete, but since automatically expands user typed tabs, the point is mostly. So I think the count_lines_with_wrapping tabwidth parameter could be replaced with a local assignment.
tabwidth = 8
and all the testing involving a 'settable' tabwidth removed.

The linewidth stuff is ugly. Tk initially calculates pixel width from configured width in characters, (average) font character width, padding. Too bad it apparently does not itself do the reverse calculaton need for squeezer.

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

@terryjreedy, following your comment on the subject, I did some timings with and without the second short-circuit check and found that it had no significant effect even in the most extreme cases it was meant to optimize. I've removed it to avoid the unnecessary complexity.

@terryjreedy

So I think the count_lines_with_wrapping() tabwidth parameter could be replaced with a local assignment, tabwidth = 8, and all the testing involving a 'settable' tabwidth removed.

Done.

I have made the requested changes; please review again.

Thanks for making the requested changes!

@terryjreedy: please review the changes made to this pull request.

I am reviewing this and making a few changes now.

That assertion still fails on AppVeyor: zero_char_width is 8 before and after the reload() call. This is despite the test requiring the "gui" resource. See traceback below.

What should we do with this?

Test the reload() class-method.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\projects\cpython\lib\idlelib\idle_test\test_squeezer.py", line 321, in test_reload
    self.assertGreater(squeezer.zero_char_width, orig_zero_char_width)
AssertionError: 8 not greater than 8```

That assertion still fails on AppVeyor

It passes locally on Windows 10, by the way.

That assertion still fails on AppVeyor

It fails on Travis-CI too :(

Do we just drop this assertion?

Cheryl's Ubuntu off-by-1 rounding failure and the CI no-change failures had different causes. I am experimenting with her suggested changes that avoid idleConf and expect to push something for the CI bots.

Whoops, hit wrong comment button.

Thank you Cheryl, your suggestion works for the CI bots. After experimentation, I expect the new code should work even if a system does not have 'Courier'. On my machine, an unknown family is replaced by a default system font (Ariel, for me) and I assume that this is universal tk behavior.

Tal, go ahead and merge.

Thanks @taleinat for the PR 🌮🎉.. I'm working now to backport this PR to: 3.7.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

GH-11541 is a backport of this pull request to the 3.7 branch.

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot x86 Gentoo Installed with X 3.x has failed when building commit 39a33e9.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/103/builds/1964) and take a look at the build logs.
4. Check if the failure is related to this commit (39a33e9) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/103/builds/1964

From https://github.com/python/cpython
 * branch                  master     -> FETCH_HEAD
Reset branch 'master'

Python/pystate.c: In function ‘_long_shared’:
Python/pystate.c:1483:18: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
     data->data = (void *)value;
                  ^

/buildbot/tmp/tmpdir/tmplub9mdym/pip-18.1-py2.py3-none-any.whl/pip/_vendor/requests/status_codes.py:3: SyntaxWarning: invalid escape sequence \o
/buildbot/tmp/tmpdir/tmplub9mdym/pip-18.1-py2.py3-none-any.whl/pip/_vendor/requests/status_codes.py:3: SyntaxWarning: invalid escape sequence \o

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot x86 Gentoo Non-Debug with X 3.x has failed when building commit 39a33e9.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/99/builds/2024) and take a look at the build logs.
4. Check if the failure is related to this commit (39a33e9) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/99/builds/2024

Traceback (most recent call last):
  File "/buildbot/buildarea/cpython/3.x.ware-gentoo-x86.nondebug/build/Lib/idlelib/idle_test/test_squeezer.py", line 310, in test_reload
    self.assertGreater(squeezer.zero_char_width, orig_zero_char_width)
AssertionError: 6 not greater than 6

----------------------------------------------------------------------

Ran 475 tests in 8.425s

FAILED (failures=1, skipped=3)


Traceback (most recent call last):
  File "/buildbot/buildarea/cpython/3.x.ware-gentoo-x86.nondebug/build/Lib/idlelib/idle_test/test_squeezer.py", line 310, in test_reload
    self.assertGreater(squeezer.zero_char_width, orig_zero_char_width)
AssertionError: 6 not greater than 6

----------------------------------------------------------------------

Ran 475 tests in 5.916s

FAILED (failures=1, skipped=3)

The problematic test_reload() is failing on the Gentoo buildbots:

======================================================================
FAIL: test_reload (idlelib.idle_test.test_squeezer.SqueezerTest)
Test the reload() class-method.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/buildbot/buildarea/cpython/3.x.ware-gentoo-x86.nondebug/build/Lib/idlelib/idle_test/test_squeezer.py", line 310, in test_reload
    self.assertGreater(squeezer.zero_char_width, orig_zero_char_width)
AssertionError: 6 not greater than 6
----------------------------------------------------------------------``

I will open a new issue and PR to fix this, initially by disabling it. I approved the backport since I will follow with the initial fix and I want 3.7 in sync with master.

Issue 35730, PR #11543.