What is the minimum set of characters with which you can write any valid python program?
I've come up with a 9-character translator using exec (also posted at this GitHub gist):

def convert_txt(txt):
    """Convert the text of a Python program to minimal Python"""
    s = "+".join(["chr(%s)" % "+".join(["1"] * ord(c))
                            for c in txt])
    return 'exec(%s)' % s


The only characters it needs are ()+1cehrx.