IDLE -s and (-, -c command, or -r file) produces error message

[pppery]

BPO	24265
Nosy	@terryjreedy, @kbkaiser, @serwy, @pppery

^{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 = 'https://github.com/terryjreedy'
closed_at = None
created_at = <Date 2015-05-22.13:16:16.379>
labels = ['expert-IDLE', 'type-bug', '3.10']
title = 'IDLE -s and (-, -c command, or -r file) produces error message'
updated_at = <Date 2020-06-07.23:28:23.292>
user = 'https://github.com/pppery'

bugs.python.org fields:

activity = <Date 2020-06-07.23:28:23.292>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2015-05-22.13:16:16.379>
creator = 'ppperry'
dependencies = []
files = []
hgrepos = []
issue_num = 24265
keywords = []
message_count = 2.0
messages = ['243824', '273523']
nosy_count = 4.0
nosy_names = ['terry.reedy', 'kbk', 'roger.serwy', 'ppperry']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'test needed'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue24265'
versions = ['Python 3.10']

[pppery]

When I run "python -m idlelib.idle -sc [command] from the command line, IDLE runs the startup file, but then pops up an error message saying "the Python Shell window is already executing a command;please wait until it is finished." When the error window is closed, the command executes, unless the main Python Shell has already been closed, in which case a traceback occurs:
Traceback (most recent call last):
  File "C:\Python27\lib\runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "C:\Python27\lib\runpy.py", line 72, in _run_code
    exec code in run_globals
  File "C:\Python27\lib\idlelib\idle.py", line 11, in <module>
    idlelib.PyShell.main()
  File "C:\Python27\lib\idlelib\PyShell.py", line 1602, in main
    shell.interp.execsource(cmd)
AttributeError: 'NoneType' object has no attribute 'execsource'

[terryjreedy]

I confirmed the bug on Win10 with 3.5 and 3.6. "python -m idlelibl -s" prints a prompt*, runs the file and prints any output, and prints a prompt. It then accepts user input. When "-c command" is added, it should accept that as user input (and perhaps display it on the input line). But I get the same error box. When clicked away, 'command' executes and a third prompt is displayed.

*Another bug. The startup file should run first, before a prompt, just as it does in python, and just as with files run with F5. It would not hurt if [Running <path>] were printed, but not a prompt. Prompts should mean 'ready to accept input'. Ditto for -c command, unless IDLE is changed to display the command after the prompt as if typed in.

Warning comes from ModifiedInterpreter (MI).dispaly_executing_dialog, which is called in MI.runcommand if 'self.tkconsole.executing'.  MI.runcommand is used for internal startup code and for '-', '-c', and '-r' on the command line, but not for user '>>> ' and editor code. 

I confirmed that '-s' + '-' or '-r' give the same warning. Hence the title change.

MI.tkconsole is the PyShell (PS) window instance. PS.executing is set/reset in PS.beginexecuting, PS.endexecuting. The latter should apparently be called someplace it is not now.