Improve IDLE's "subprocess didn't make connection" message

[roseman]

BPO	25514
Nosy	@terryjreedy, @kbkaiser, @serwy, @roseman, @willingc
PRs	bpo-25514: Improve IDLE's connection refused message #2177 bpo-25514: Improve IDLE's connection refused message (#2177) #2178

^{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 2015-10-29.20:47:20.690>
labels = ['easy', 'expert-IDLE', 'type-feature', '3.7', 'docs']
title = 'Improve IDLE\'s  "subprocess didn\'t make connection" message'
updated_at = <Date 2018-09-07.21:42:46.760>
user = 'https://github.com/roseman'

bugs.python.org fields:

activity = <Date 2018-09-07.21:42:46.760>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['Documentation', 'IDLE']
creation = <Date 2015-10-29.20:47:20.690>
creator = 'markroseman'
dependencies = []
files = []
hgrepos = []
issue_num = 25514
keywords = ['easy']
message_count = 17.0
messages = ['253693', '253694', '253695', '253704', '253705', '253706', '253745', '253833', '255578', '258498', '295369', '295937', '295950', '295972', '295975', '295977', '324800']
nosy_count = 7.0
nosy_names = ['terry.reedy', 'kbk', 'roger.serwy', 'markroseman', 'docs@python', 'willingc', 'lac']
pr_nums = ['2177', '2178']
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue25514'
versions = ['Python 3.6', 'Python 3.7']

[roseman]

When we create e.g. string.py that shadows a stdlib module needed by IDLE, it would be nice if a better error message could be shown, pointing to that cause.

Original message:

lac at smartwheels:~/junk$ echo "print ('hello there')" >string.py
lac at smartwheels:~/junk$ idle-python3.5
hello there
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3.5/idlelib/run.py", line 10, in <module>
    from idlelib import CallTips
  File "/usr/lib/python3.5/idlelib/CallTips.py", line 16, in <module>
    from idlelib.HyperParser import HyperParser
  File "/usr/lib/python3.5/idlelib/HyperParser.py", line 14, in <module>
    _ASCII_ID_CHARS = frozenset(string.ascii_letters + string.digits + "_")
AttributeError: module 'string' has no attribute 'ascii_letters'

IDLE then produces a popup that says:

IDLE's subprocess didn't make connection. Either IDLE can't stat a subprocess por personal firewall software is blocking the connection. <ok>

--------

I think that life would be a whole lot easier for people if instead we got
a message:

Warning: local file /u/lac/junk/string.py shadows module named string in the
Standard Library

I think that it is python exec that would have to do this -- though of
course the popup could also warn about shadowing in general, instead of
sending people on wild goose chases over their firewalls.

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

Laura, I think what you want should actually be more-or-less doable in IDLE.

The main routine that starts IDLE should be able to detect if it starts correctly (something unlikely to happen if a significant stdlib module is shadowed), watch for an attribute error of that form and try to determine if shadowing is the cause, and if so, reissue a saner error message.

The subprocess/firewall error is occurring because the ‘string’ problem in your example isn’t being hit right away so a few startup things already are happening. The point where we’re showing that error (as a result of a timeout) should be able to check as per the above that IDLE was able to start alright, and if not, change or ignore the timeout error.

There’ll probably be some cases (depending on exactly what gets shadowed) that may be difficult to get to work, but it should be able to handle most things.

See full thread starting at https://mail.python.org/pipermail/python-dev/2015-October/142061.html

[lac]

Note that the full path name of the file that is doing the shadow
is of important interest to teachers. We get machines will all sorts of garbage written on them -- the amount of hell caused by a misnamed turtle.py is hard to measure -- and anything as helps in the finding of the file as needs removing or renaming will be eternally welcome.

[lac]

s/machines will/machines with/

(I was tired.)

[terryjreedy]

Laura, I did not understand from your python-list post that you were complaining about shadowing disabling IDLE itself, as opposed to user code. That is partly because you followed up on Peter Otten complaining because IDLE tries to run user code the same way that python does.

The solution for IDLE itself is for IDLE to do what python does on startup, which is to ensure that the stdlib modules it needs are indeed imported from the stdlib. I presume that python only prepends '' to sys.path *after* it does its imports. Example:

>>> import sys; list(sys.modules)
[..., abc, ...]
C:\Users\Terry>echo "print('abc')" >abc  # verified with dir
C:\Users\Terry>python
>>> >>> import sys; sys.modules['abc'].__file__
'C:\\Programs\\Python35\\lib\\abc.py'

So IDLE should remove sys.path[0] from sys.path and, in the user process, restore it only after normal imports. Ignore -n single process mode for now.

Aside from this, the popup message needs to be changed, but better that it occur less often (by the fix above) or never (by switching to pipes?).

As for user code: I have in mind that there should be a doc how-to about tracebacks and exception messages, with a sections giving possible explanations and remedies for specific messages, such as the above. This I would make messages like the above a link to the how-to entry. In the meanwhile, we could consider a special case search of error message lines.

-I just noticed that this issue is the result of a pydev thread. Off to read that.

[terryjreedy]

"I think that removing '' from sys.path, so that IDLE can run, is better than a nicer warning that it cannot run. This, of course, requires that sys not be shadowed, so that sys.path can be accessed." So after importing sys, we should check sys.__file__, or do the manipulation in try: except: <post error message>. This will be part of a much more careful startup sequence.

[terryjreedy]

Either tkinter and tkinter.messagebox or subprocess must be imported to display a message when IDLE is started from an icon, and there is no console. With subprocess, '''python -i -c "print('Cannot start IDLE (or whatever)')"''' should work. If nothing else, this would be a way to display a message when import tkinter fails.

[lac]

Re: misunderstanding

Sorry Terry. From my end the great 4 day "weekend of mail.python.org needs to be rebuilt from scratch" happened precisely as I was about
to reply to your post. The reply to Peter Otten showed up later
as part of my mailer agent trying to send the thing every 4 hours for
a week. So confusion reigns.

[lac]

can I send a file

[lac]

webmaster got another one of these today.