def splitLast(myString, chunk):
    """
    returns a tuple of two strings, splitting the string at the last occurence of a given chunk.
    >>> splitLast('hello my dear friend', 'e')
    ('hello my dear fri', 'nd')
    """
    p = myString.rfind(chunk)
    if p > -1:
        return myString[0:p], myString[p + len(chunk):]
    else:
        return myString, ''