IDLE 'strip trailing whitespace' changes multiline strings

[mr-nfamous]

BPO	31477
Nosy	@terryjreedy, @mr-nfamous

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = <Date 2017-09-15.21:58:02.491>
created_at = <Date 2017-09-14.19:59:30.290>
labels = ['expert-IDLE', 'type-bug', '3.7']
title = "IDLE 'strip trailing whitespace' changes multiline strings"
updated_at = <Date 2017-09-15.21:58:02.490>
user = 'https://github.com/mr-nfamous'

bugs.python.org fields:

activity = <Date 2017-09-15.21:58:02.490>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = True
closed_date = <Date 2017-09-15.21:58:02.491>
closer = 'terry.reedy'
components = ['IDLE']
creation = <Date 2017-09-14.19:59:30.290>
creator = 'bup'
dependencies = []
files = []
hgrepos = []
issue_num = 31477
keywords = []
message_count = 2.0
messages = ['302204', '302274']
nosy_count = 2.0
nosy_names = ['terry.reedy', 'bup']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue31477'
versions = ['Python 3.6', 'Python 3.7']

[mr-nfamous]

This function is supposed to be purely cosmetic. It just cleans up the junk whitespace commonly left behind when coding. But it could cause a problem when someone expects some string they defined to stay the same value, and then use that function and all of a sudden they have a crazy bug that you wouldn't even know how to find.

[terryjreedy]

The current behavior of IDLE's feature is standard, not a bug. The cpython respository does not currently accept .py, .c, or .rst files with any trailing whitespace. <pythondir>/tools/scripts/patchcheck.py strips trailing whitespace from all lines. Notepad++, a widely used multi-language Windows programmer's editor, does the same.

I am aware of the potential surprise.  If one wants multiline strings with embedded trailing whitespace, one should avoid trailing whitespace strippers or use Python's string concatenation feature. 
>>> s = ('space \n' 'tab\t\n' 'line3\n')
>>> s
'space \ntab\t\nline3\n'

I am revising the doc to make the rstring behavior clearer.