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Add rstrip() to the Format menu.
Python's svn repository no longer accepts files with trailing whitespace
and it is often necessary to run reindent.py before submitting. It
would be nice to have this as a built-in formatting tool.

If the interactive interpreter did not require blank lines within blocks
to have at least one 'trailing' space to avoid prematurely ending the
block (as when copy from editor window and paste), IDLE could
automatically rstrip lines. Given that that should not be done, a menu
item would be nice.

Here's an extension that adds rstrip() to the Format menu.

Applied in r72999. Will backport to 2.7.

Backported in r73001 

This has been closed but why not promote reindent.py to a module and add
an option on IDLE to allow a complete reindent.py run ?

reindent.py is very much a script: It lacks a nice, full programmatic API, I mean standalone functions to check a file object or a filename and functions implementing the command-line interface. As it is now, you see for example print calls in the middle of functions, so it’s not usable as a module.
Maybe bring this to python-dev or -ideas?

There's no need to go to python-dev or python-ideas with this one. If someone wants to figure-out a way to add reindent functionality to IDLE, patches are welcome.

I grabbed the core of reindent.py and put it into an extension, unmodified. 
The original reindent.py will emit Indentation Errors if they exist. 
ScriptBinding already has nice code to handle these problems by highlighting the error, placing the cursor at the error, and presenting a message box. Rather than duplicate this code, this extension makes calls into ScriptBinding to check for syntax errors when the core reindent code throws exceptions.

Opened back up for the new patch (posted after the previous close).

The code needs to be updated for Python 3 and it needs a test. I'm deassigning it in the hopes that someone will feel free to pick it up.

I use rstrip routinely when editing idlelib files, before committing, so it has been useful for that purpose.
I do not happen to know what reindent.py does that the current format options do not.
#18704 was about integrating the pep8 style checker. That was closed in favor of adding a generic facility to run external analysis tools. There is not an open issue for that yet, but I expect it to happen, perhaps this summer. Reindent.py, if maybe improved, might be a candidate, though I will also try to look at the patch sometime.

One other thought, it would be nice if there were an option (on by default) to automatically strip trailing whitespace when a file is saved. That would be much nicer than making the user remember to do periodic clean-ups as they edit.

Having occasionally forgotten, and had to do whitespace commits, I agree. For Python code, there is never an absolute need for trailing whitespace. Trailing whitespace in string literals can be done by parse time concatenation.
'''\
line 1
line 2
''' 'line with trailig space '
Indeed, the trick is needed to mark the trailing space in the code.
I have thought about removing trailing spaces after each return, but pasting may be a problem.

reindent.py does the following:
1. Change Python (.py) files to use 4-space indents and no hard tab characters. IDLE editor does this by default, as do other programming editors, except as PEP8 recommends something else for continuation lines within fences <(), [], {}>. Before doing anything with reindent, I would want to check whether it messes with IDLE;s smart indents.
The format module and Format menu has functions to add/remove tabs and changes space indents, as well as rewrap.
The only thing left is dealing with a messed up file, but suspect that this is rarer than 19 (1st public version of reindent.py) or even 10 years ago (this issue). Is this issue still needed?
2. Trim excess spaces and tabs from ends of lines. Format => strip whitespace, added on this issue, does this. (The code is now in the format module.)
3. Remove empty lines at the end of files. Rstrip should do this but does not. This is a separate issue from reindenting.
4. Ensure that the last line ends with a newline. Save in iomenu ensures this, but this should be part of 'strip whitespace', especially if we 'rstrip' on save (#33046).

Adding rstrip as it was then was done over a decade ago, and this issue was closed then. Improvements, as discussed immediately above have been added with other issues, or will be. I am rejecting the add-on idea of incorporating reindent.py as unneeded. (It should have been a new issue instead of re-opening this one.)