Setting up the same commit checks locally that the main repo enforces for incoming patch sets can save a great deal of frustration with the server rejecting "hg push" for changes (this can be especially frustrating if you have already merged changes across branches).

The committer section of the devguide [1] should explain how to:

1. Check out the hooks repo from hg.python.org
2. Configure the whitespace checking hook by adding this to hgrc for the relevant repo(s) (adjusting the path appropriately for the checked out location of the hooks repo):

[hooks]
commit = python:~/devel/hg_hooks/checkwhitespace.py:check_whitespace_single


[1] http://docs.python.org/devguide/committing.html#committing-and-pushing-changes