def parse(sentence):
    """
    Removes everything but alpha characters and spaces, transforms to lowercase
    :param sentence: the sentence to parse
    :return: the parsed sentence
    """
    # re.sub(r'([^\s\w]|_)+', '', sentence)
    # return sentence.lower()#.encode('utf-8')
    # re.sub("^[a-zA-Z ]*$", '', sentence.lower().replace("'", ""))
    whitelist = set('abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ')
    return ''.join(filter(whitelist.__contains__, sentence)).lower()