def METHOD_NAME(access_string):
    '''Convert a string (e.g. "read") into the corresponding
    AccessType enum value (AccessType.READ).
    :param str access_string: Access type as string.
    :returns: Corresponding AccessType enum.
    :Raises: ValueError if access_string is not a valid access type.
    '''
    for access in AccessType:
        if access.name == access_string.upper():
            return access
    valid = [str(access).lower() for access in AccessType]
    raise ValueError(f"Unknown access type '{access_string}'. "
                     f"Valid values are {valid}.")