def prune_multiple_spaces(mystring: str):
    """ Prune multiple spaces in a sentence and replace with single space
    Parameters:
    -----------
    sentence: Sentence string with mulitple spaces

    Returns:
    --------
    cleaned_sentence: String with only single spaces.
    """

    mystring = mystring.strip()
    tokens = mystring.split(' ')
    tokens = [t for t in tokens if t != '']
    if len(tokens) == 1:
        return tokens[0]
    else:
        return ' '.join(tokens)