IDLE: require encoding argument for textview.view_file

[terryjreedy]

BPO	32837
Nosy	@terryjreedy, @miss-islington
PRs	bpo-32837: IDLE - require encoding argument for textview.view_file. #5646 [3.7] bpo-32837: IDLE - require encoding argument for textview.view_file. (GH-5646) #5647 [3.6] bpo-32837: IDLE - require encoding argument for textview.view_file. (GH-5646) #5648

^{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 = <Date 2018-02-13.06:28:23.918>
created_at = <Date 2018-02-12.22:07:39.772>
labels = ['3.8', 'expert-IDLE', 'type-bug', '3.7']
title = 'IDLE: require encoding argument for textview.view_file'
updated_at = <Date 2018-02-13.06:28:23.917>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2018-02-13.06:28:23.917>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = True
closed_date = <Date 2018-02-13.06:28:23.918>
closer = 'terry.reedy'
components = ['IDLE']
creation = <Date 2018-02-12.22:07:39.772>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 32837
keywords = ['patch']
message_count = 4.0
messages = ['312085', '312087', '312089', '312090']
nosy_count = 2.0
nosy_names = ['terry.reedy', 'miss-islington']
pr_nums = ['5646', '5647', '5648']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue32837'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[terryjreedy]

Built-in open has an encoding parameter whose default value depends on the system: 'ascii' for some POSIX locales; 'latin1' or similar for most Windows sold in the USA or western Europe; and ???. In idlelib.textview, the signature for view_file currently includes 'encoding=None'. There have been 2 issues, bpo-32826 and another, about tests using the default failing because of 'Löwis' on line 27 of CREDITS.txt. It therefore seems an error for a global cross-platform application to use the default encoding.

To prevent this, we should remove '=None' from the encoding part of the view_file definition and make view_file calls explicitly pass an encoding. For IDLE itself, this will be 'ascii' or 'utf-8'.

This expands upon a note by Cheryl Sabella in bpo-32826 about one of the three calls that fail with the change until fixed.

I will not default to 'utf-8' because 'ascii' catches erroneous non-ascii characters in ascii-only files. For instance, a draft of README.txt was prepared with an editor that replaced ascii " and " with left and right quotes. I will not restricting the encoding otherwise because there might be external uses of the file that use other encodings.

PR to follow as soon as I get bpo number.

[terryjreedy]

New changeset 688722c by Terry Jan Reedy in branch 'master':
bpo-32837: IDLE - require encoding argument for textview.view_file. (GH-5646)
688722c

[miss-islington]

New changeset 65c32bb by Miss Islington (bot) in branch '3.7':
bpo-32837: IDLE - require encoding argument for textview.view_file. (GH-5646)
65c32bb

[miss-islington]

New changeset 9fad857 by Miss Islington (bot) in branch '3.6':
bpo-32837: IDLE - require encoding argument for textview.view_file. (GH-5646)
9fad857