import string


def _preprocess_text(text):
    """
    Removes punctuation and converts a string to lowercase
    :param text: input text to preprocess
    :return: string which has no punctuation and is lower case
    """
    exclude = set(string.punctuation)
    no_punctuation = ''.join(ch for ch in text if ch not in exclude)
    return no_punctuation.lower()