human
Complete this python program:
def lower_key(fn):
assistant
#Here is the Python code you requested.

    """:param fn: a key function
    :return:
    a function that wraps around the supplied key function to ensure
    the returned key is in lowercase.
    """
    def lower(key):
        try:
            return key.lower()
        except AttributeError:
            return key
    return process_key(lower, fn)