def cast_main_key(data):
    """
    Cast the main_key_name in a dictionary ``{main_key_name: {main_key_1 : {…}, maine_key_2 : {…}}}``

    a main_key_name is the name for all the main_keys

    Parameters
    ----------
    data : dict
        the dictionary to cast the main_key_name from

    Returns
    -------
    data : dict
        the input data with the main_keys as new top_level keys of dictionary `{main_key_1 : {…}, maine_key_2 : {…}}`
    main_key_name : str
        the name of the main_keys that got casted
    """
    if not isinstance(data, dict):
        raise TypeError("Expected type dict, got {}".format(type(data)))
    if len(data.keys()) != 1:
        received_top_level_keys = set()
        i = 0
        for key in data:
            received_top_level_keys.add(key)
            i += 1
            if i == 3:
                break
        raise ValueError(
            f"Dict has more than one key, received e.g. '{received_top_level_keys}'. "
            "Please provide either the main_element for dicts with more than one entry or "
            "provide dict with only one key"
        )

    [main_key_name] = data.keys()
    [data] = data.values()
    return data, main_key_name