def check_string_length(value, name=None, min_length=0, max_length=None):
    if not isinstance(value, six.string_types):
        if name is None:
            msg = _("The input is not a string or unicode")
        else:
            msg = _("%s is not a string or unicode") % name
        raise exception.InvalidInput(message=msg)

    if name is None:
        name = value

    if len(value) < min_length:
        msg = _("%(name)s has a minimum character requirement of "
                "%(min_length)s.") % {'name': name, 'min_length': min_length}
        raise exception.InvalidInput(message=msg)

    if max_length and len(value) > max_length:
        msg = _("%(name)s has more than %(max_length)s "
                "characters.") % {'name': name, 'max_length': max_length}
        raise exception.InvalidInput(message=msg)
Check the length of specified string
dataset/ETHPy150Open BU-NU-CLOUD-SP16/Trusted-Platform-Module-nova/nova/utils.py/check_string_length