Bug report

Bug description:

IDLE aborts at startup with a traceback instead of degrading gracefully when a user configuration file (~/.idlerc/config-*.cfg) cannot be parsed.

idlelib.config.IdleConfParser.Load calls configparser's read_file with no error handling, so a configparser.Error such as a MissingSectionHeaderError from a partially written file (for example one left behind by an interrupted Save) propagates out of IdleConf.LoadCfgFiles and stops IDLE from opening. The user then has to find and delete the file by hand.

The config.py module docstring states that the configuration system is meant to degrade gracefully rather than fail.

Reproduction

import os, tempfile
from idlelib import config

with tempfile.TemporaryDirectory() as d:
    path = os.path.join(d, 'config-main.cfg')
    with open(path, 'w', encoding='utf-8') as f:
        f.write('option = value\n')   # missing section header
    config.IdleConfParser(path).Load()

On the main branch this raises:

configparser.MissingSectionHeaderError: File contains no section headers.
file: '.../config-main.cfg', line: 1
'option = value\n'

The same happens for a real profile inside IdleConf.LoadCfgFiles() during startup, so IDLE will not open until the file is removed.

Suggested fix

Catch configparser.Error in IdleConfParser.Load, warn to stderr, and fall back to the default configuration, matching the documented behavior.

CPython versions tested on:

3.16, CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-153477: Fix IDLE startup crash on a corrupt user config file #153478