def string(message, err='Please provide an input.'):
    """Command line input and error checking for strings (error if blank).

    Args:
        message (str): The input message displayed in the command line.
        err (str, optional): The message displayed for an erroneous input.
            Defaults to "Please provide an input.".

    Returns:
        str: The first sucessfully input string.
    """
    while True:
        data = input(message)
        if data.strip() == '':
            print(err)
            continue
        return data
