If that's the actual code you're using, it has a bug:  the "if k2[1] is None" test is useless, since regardless of whether it's true or false, the next `if` suite overwrites `retval`.  You probably meant

    elif k1[1] ...
    ^^

instead of

    if k1[1] ...

Does that fix your problem?

If not, please augment the bug report with the _complete_ code you're actually using, a sample problematic input, the exact output you're expecting, and the exact output you're seeing instead.  We're not telepathic ;-)