def chars_to_bin(string):
    """
    Convert characters of a string to a 7 bits long binary format
    """
    #return ['{:b}'.format(ord(character)) for character in string]

    list_of_7bits_items = ['{:b}'.format(ord(character)) for character in string]

    if len(list_of_7bits_items)<8:
        for i in range (8 - len(list_of_7bits_items)):
            list_of_7bits_items.append('{0:07b}'.format(ord(' ')))

    return list_of_7bits_items