def is_valid(glyph_str):
    """ Validates if glyph_str is alphanumeric and contains unique chars

    Parameters
    ----------
    glyph_str : string
        glyph alphabet to be used for number encoding

    Returns
    -------
    True when:
        glyph string is alphanumeric
        Each char occurs only once

    """
    uniq = True
    if len({x for x in glyph_str}) != len(glyph_str):
        uniq = False

    return uniq and glyph_str.isalnum()