Idle: stop depending on console output

[terryjreedy]

BPO	18318
Nosy	@terryjreedy, @ned-deily, @serwy, @roseman

^{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 2013-06-27.22:43:29.439>
labels = ['expert-IDLE', 'type-bug', '3.10']
title = 'Idle: stop depending on console output'
updated_at = <Date 2020-06-07.23:27:02.960>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2020-06-07.23:27:02.960>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2013-06-27.22:43:29.439>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 18318
keywords = []
message_count = 3.0
messages = ['191966', '192087', '192094']
nosy_count = 5.0
nosy_names = ['terry.reedy', 'ggenellina', 'ned.deily', 'roger.serwy', 'markroseman']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'test needed'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue18318'
versions = ['Python 3.10']

[terryjreedy]

It appears that Idle was originally written to run on *nix after being launched from a command-line console. Messages related to Idle code (warnings and exceptions) are sent back to the console, while messages related to user code go to the shell window. This makes Idle a hybrid text/gui application.

Later, Idle was ported to run on Windows with the pythonw.exe no-console binary. When it is started normally for Windows, from anything but a console, there is no console. This has caused problems when Idle tries to write to the non-existent console. (I do not know the situation on modern Mac and *nix.) (Even when a console does exist, it will usually get buried and messages may not be seen.)

Example: The warning system, monkey patched in both PyShell.py and run.py and documented in the former. (Edited quote from 3.3.)

# Override warnings module to write to warning_stream.
# Initialize to send IDLE internal warnings to the console.
# ScriptBinding.check_syntax() will temporarily redirect the stream
# to the shell window to display warnings when checking user's code.
warning_stream = sys.__stderr__  # Typically None, at least on Windows.
def idle_showwarning(...
    ...
    if file is None:
        file = warning_stream  # Which may itself be None!!!
    try:
        file.write(...  # AttributeError when file is still None
    except OSError:
        pass  # if file (probably __stderr__) is invalid, skip warning.

The patch for #62281 also catches AttributeError as a bandage.

[EDIT 2023 May 6: None.write AttributeError is now also caught. An alternative, used in config.py, is print(..., file=sys....).]

Issue goal: make Idle a true gui app by removing the dependence on a console, which may not exist.

Proposed method: re-factor Idle startup to try to import tkinter first, rather than last.

If this import fails, inform user with console message and/or the os-specific means to gui apps to tell users 'I cannot start because ...'. I know this exists on Windows because I have seen such messages. I presume same is true on other systems.

If this import succeeds, setup traceback and warnings hooks to send internal messages to a gui messagebox rather than (or possibly in addition to) a console that may or may not be present. Or send the messages to the Shell window, but marked somehow as internal. The warnings hook might be used after importing non-Idle modules but before importing Idle modules, so startup is not bogged down on debug builds by DeprecationWarnings from non-Idle modules

To be a good citizen for testing, all custom hooks should be undone before the PyShell import finishes and before PyShell.main exits (same for run.py).

[serwy]

This looks similar to #57791 with the patch to redirect console writes to a GUI text box.

[terryjreedy]

The proposal here is to flip the roles of text console and graphics gui, rather than to indefinitely bandage the current roles. I would want that even with the patch for #57791 applied (which I hope can be done soon).

[arhadthedev]

Later, Idle was ported to run on Windows with the pythonw.exe no-console binary. When it is started normally for Windows, from anything but a console, there is no console. This has caused problems when Idle tries to write to the non-existent console.

This point will be fixed by gh-101802.

I agree with the rest, though.