Reformats the column string to make sure it contains only numerical, letter characters or underscore.

    :param column: column name to be reformatted
    :type column: str
    :return: column name with illegal characters removed
    :rtype: str

def col_name2cat(column):
    """
    Reformats the column string to make sure it contains only numerical, letter characters or underscore.

    :param column: column name to be reformatted
    :type column: str
    :return: column name with illegal characters removed
    :rtype: str
    """
    column_string = ''.join(s for s in column.replace(' ', '_') if s.isalnum() or '_' == s)
    return column_string