On http://mail.python.org/pipermail/python-dev/2008-November/083732.html
Nicole King wrote:

"""
I found I needed support for taint mode in python and have done some
work to realise this. It's by no means complete at this time, but I'm
floating this idea on this group to see how much interest there is.

The implementation is pretty simple:

- an extra field in PyObject to maintain the taint status
- a couple of extra functions __gettaint__() that returns the taint
status and __settaint__(value) that sets the taint value, returning the
previous status
- an additional command-line flag -a and environment variable
PYTHONIGNORETAINT that suppress taint checking
- a few macros defined in Objects/object.h to support taint management
- a new built-in exception, PyExc_TaintError, for reporting operations
on tainted objects
"""

More information and download: http://www.cats-muvva.net/software/