def data_type_dict():
    """Returns a dictionary from data type string to the data type.

    The dictionary should include at least:
    float16
    float32
    float64
    uint8
    int8
    int16
    int32
    int64

    This function will be called only *once* during the initialization fo the
    backend module. The returned dictionary will become the attributes of the
    backend module.

    Examples
    --------
    >>> import torch as th
    >>> def data_type_dict():
    >>>   return { 'float16' : th.float16, 'float32' : th.float32, ... }

    After the module is initialized.

    >>> import backend as F
    >>> F.float16  # this will point to torch.float16

    Returns
    -------
    dict of str to data type
        The data type dict.
    """
    pass
