IDLE should catch user config file UnicodeDecodeError

[ghost]

BPO	40435
Nosy	@terryjreedy
Files	pic04-29-18-05-10.png: error message config-main.cfg: config-main.cfg

^{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 2020-04-29.10:05:36.253>
labels = ['expert-IDLE', 'type-bug', '3.7']
title = 'IDLE should catch user config file UnicodeDecodeError'
updated_at = <Date 2020-04-30.05:53:53.966>
user = None

bugs.python.org fields:

activity = <Date 2020-04-30.05:53:53.966>
actor = '\xe5\xb7\xa6\xe8\xbf\x9f'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2020-04-29.10:05:36.253>
creator = '\xe5\xb7\xa6\xe8\xbf\x9f'
dependencies = []
files = ['49099', '49101']
hgrepos = []
issue_num = 40435
keywords = []
message_count = 5.0
messages = ['367639', '367642', '367644', '367703', '367739']
nosy_count = 2.0
nosy_names = ['terry.reedy', '\xe5\xb7\xa6\xe8\xbf\x9f']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'test needed'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40435'
versions = ['Python 3.7']

[ghost]

Environment:
1.OS:
Windows 10 1909 Pro
2.Python version:
3.7.4 (default, Aug 9 2019, 18:34:13) [MSC v.1915 64 bit (AMD64)]
3.Error message:
UnicodeDecodeError: 'CP_UTF8' codec can't decode byte 0xd0 in position 23: No mapping for the Unicode character exists in the target code page

How to reporduce?
Set the code page to UTF-8 in windows control pannel/region/
Type idle in the terminal hoping to launch the IDLE, but you will get the error.

[terryjreedy]

The uploaded .png has the traceback. (Pasting it into the post would have been fine and a bit easier for all of us.) The error occurred when IDLE's config tried to load the user config files, ~/.idlerc/config-xyz.cfg. (~ is usually C:/Users/yourname.) configparser.read opens the files with the default 'encoding=None', which uses the current system default. This failed with the error given. Either there is a byte error in one of the files or you customized IDLE with a non-ascii character before switching to utf-8, if indeed you switched.

In either case, the reading error does not appear to be an IDLE bug. However, IDLE should catch UnicodeDecodeError, tell the user which file could not be read and how it failed, and move on as if it were not there.

Serhiy: Codec CP_UTF8 is not listed in https://docs.python.org/3.7/library/codecs.html#standard-encodings. Should it be? Any other comments?

左迟: On my American machine, I can open Control Panel, select Clock and Region, Region, Administrative tab, and there is a button for 'Change system local...'. It pops up a box with a checkbox "[] Beta: Use Unicode UTF8 for worldwide language support." Is this what you meant, and/or what you did?

If the user config files were only written by IDLE, they could always be uft-8 encoded. However, users were once told to edit by hand, and there are still cased when they do, and for some things like loading custom keysets, it is quite appropriate.