Clean up trailing whitespaces in sources

My editor (emacs) is configured to remove trailing whitespaces in python files when I save them. This way I never commit modifications related to whitespaces changes, making the diffs readable since they contain relevant modifications only.

Unfortunately not everyone do that, and when it comes to contributing to an existing project it can be very difficult to produce readable patches: sometimes while the actual patch is just a one line change the diff will show dozens of blank changes, due to whitespaces clean up.

Diff has a switch to ignore whitespace changes, but this is incompatible with python: if you change the block level (indentation) it is just ignored.

To clean up all python files found under a directory I use a shell one-liner:

$ find . -name '*.py' -exec sed -i {} -e 's/[ \t]*$//' ';'

As usual it worked-for-me™ but comes with no warranty.

My workflow for contributing a clean patch is like this:

1. create a local branch with bazaar, mercurial or git. Of course it depends if the project is already using one of them, but if you branch from a subversion repository it's just a matter of preferences
   
2. clean whitespaces and commit (locally)
3. create and submit the patch normally
   

And here is the related configuration part for emacs:

;; whitespace cleanup
(defun my-py-no-trailing-space ()
; this hook is buffer local, can't add it globaly
(add-hook 'write-contents-functions 'delete-trailing-whitespace)
; if enabled, clear buffer at load time (this will automatically put the buffer in modified state, it might be annoying)
;(whitespace-cleanup)
)

(add-hook 'python-mode-hook 'my-py-no-trailing-space)

I believe that other editors and environments (including Eclipse) can be configured for this, too.