def depunct(s):
    """
    Returns s but with everything that is not a letter
    removed

    Parameter: s the string to edit
    Precondition s is a string
    """
    assert type(s) == str, repr(s) + ' is not a string'     # get in the habit


    # Work on small data  (BASE CASE)
    if s == '':
        return s

    # Break up the data   (RECUSIVE CASE)
    left = s[0]
    if not s[0].isalpha():
        left = ''
    right = depunct(s[1:])

    # Combine the results
    return left+right