def alphabets_input(min_length=None, max_length=None,
                    description="", filter_null=True):
    """
    Read a string from standard. And filter input by length.

    If length of input is out of defined length, read a string again.

    Parameters
    ----------
    min_length : int
        Minimum length of input. None means no minimum length.
    max_length : int
        Maximum length of input. None means no maximum length.
    description : str
        Use like input(description)
    filter_null : bool
        If return input "". If False and input equals "", read again.

    Returns
    -------
    alphabets_input : str
        Only alphabet string or "" (only if filter_null is False).

    """
    while True:
        inputs = input(description)
        if not filter_null and len(inputs) == 0:
            return ""
        if inputs.isalpha():
            if min_length is not None and len(inputs) < min_length:
                continue

            elif max_length is not None and len(inputs) > max_length:
                continue

            return inputs
        else:
            pass