@roseman, thanks for your PR! By analyzing the history of the files in this pull request, we identified @kbkaiser, @terryjreedy and @ned-deily to be potential reviewers.

Turn Debugger on, Run file, and
Traceback (most recent call last):
File "F:\Python\mypy\tem2.py", line 1, in
import Tkinter as tk
File "F:\Python\mypy\tem2.py", line 1, in
import Tkinter as tk
File "f:\dev\3x\lib\bdb.py", line 86, in trace_dispatch
return self.dispatch_line(frame)
File "f:\dev\3x\lib\bdb.py", line 110, in dispatch_line
self.user_line(frame)
File "f:\dev\3x\lib\idlelib\debugger.py", line 32, in user_line
self.gui.interaction(message, frame)
AttributeError: 'PyShellFileList' object has no attribute 'already_open'

Thanks Terry. I've added the missing routine to filelist.py in my branch. It looks like this is automatically added to this pull request...? (excuse the newbie question)

Yes, when one pushes a commit to a branch on a github repository that is the basis for a pull request, then the commit appears on the pull request. You probably pushed to 'origin'. If I created a local pr_2454 branch and made some commits, and did 'git push https://github.com/roseman pr_2454:debugger-ui-17942', those commits would become part of this. Please ask questions. The devguide is both helpful and confusing.

To try and help move older pull requests forward, we are going through and backfilling 'awaiting' labels on pull requests that are lacking the label. Based on the current reviews, the best we can tell in an automated fashion is that a core developer requested changes to be made to this pull request.

If/when the requested changes have been made, please leave a comment that says, I have made the requested changes; please review again. That will trigger a bot to flag this pull request as ready for a follow-up review.

From AppVeyor

C:\projects\cpython\lib\idlelib\debugger.py:316: DeprecationWarning: invalid escape sequence \.
  match = re.match('^<(?:.*)\.([^\.]*) object at 0x[0-9a-f]+>$'

Add 'r' prefix to regex

ERROR: test_init (idlelib.idle_test.test_debugger.NameSpaceTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\projects\cpython\lib\idlelib\idle_test\test_debugger.py", line 25, in test_init
    debugger.NamespaceViewer(self.root, 'Test')
AttributeError: module 'idlelib.debugger' has no attribute 'NamespaceViewer'

replaced by newer PR