IDLE: Saving Shell should not add \n

[terryjreedy]

BPO	26353
Nosy	@terryjreedy, @ZackerySpytz, @miss-islington, @miss-islington
PRs	bpo-26353: IDLE adds an unneeded newline when saving a shell window #17103 [3.8] bpo-26353: IDLE adds an unneeded newline when saving a shell window (GH-17103) #17118 [3.7] bpo-26353: IDLE adds an unneeded newline when saving a shell window (GH-17103) #17119

^{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 2019-11-12.11:14:07.956>
created_at = <Date 2016-02-12.22:08:12.778>
labels = ['3.8', 'expert-IDLE', 'type-bug', '3.7', '3.9']
title = 'IDLE: Saving Shell should not add \\n'
updated_at = <Date 2019-11-14.07:35:51.566>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2019-11-14.07:35:51.566>
actor = 'ZackerySpytz'
assignee = 'terry.reedy'
closed = True
closed_date = <Date 2019-11-12.11:14:07.956>
closer = 'terry.reedy'
components = ['IDLE']
creation = <Date 2016-02-12.22:08:12.778>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 26353
keywords = ['patch']
message_count = 6.0
messages = ['260205', '356423', '356436', '356441', '356442', '356583']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'ZackerySpytz', 'miss-islington', 'miss-islington']
pr_nums = ['17103', '17118', '17119']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue26353'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[terryjreedy]

When one saves the IDLE Shell window, at least when the cursor is at the prompt, \n is added, so that

>> |

changes to

>>
|

This seems wrong. It does not happen in editor windows. I should check Output Windows.

[terryjreedy]

Zachary determined that the issue is that writing calls iomenu.IOBinding.fixlastline, which unconditionally adds \n at the end if there is one. That is not needed for the Shell and wrong when it ends with a prompt, which is the normal case.

[terryjreedy]

New changeset c8b53dc by Terry Jan Reedy (Zackery Spytz) in branch 'master':
bpo-26353: IDLE adds an unneeded newline when saving a shell window (GH-17103)
c8b53dc

[miss-islington]

New changeset 177b126 by Miss Islington (bot) in branch '3.7':
bpo-26353: IDLE adds an unneeded newline when saving a shell window (GH-17103)
177b126

[miss-islington]

New changeset 8ce1a9c by Miss Islington (bot) in branch '3.8':
bpo-26353: IDLE adds an unneeded newline when saving a shell window (GH-17103)
8ce1a9c

[ZackerySpytz]

Thank you, Terry, for modifying the PR and merging it.