def clean_doi(doi_string):
    """
    Use regex to extract all DOI ids from string (i.e. 10.1029/2005pa001215)

    :param str doi_string: Raw DOI string value from input file. Often not properly formatted.
    :return list: DOI ids. May contain 0, 1, or multiple ids.
    """
    regex = re.compile(r'\b(10[.][0-9]{3,}(?:[.][0-9]+)*/(?:(?!["&\'<>,])\S)+)\b')
    try:
        # Returns a list of matching strings
        m = re.findall(regex, doi_string)
    except TypeError as e:
        # If doi_string is None type, return empty list
        print("TypeError cleaning DOI: {}, {}".format(doi_string, e))
        m = []
    return m
Use regex to extract all DOI ids from string (i.e. 10.1029/2005pa001215)

    :param str doi_string: Raw DOI string value from input file. Often not properly formatted.
    :return list: DOI ids. May contain 0, 1, or multiple ids.