Why can't I import masked_cross_entropy?

In seq2seq-translation-batched.ipynb, the import of masked_cross_entropy seems not worked.
When I execute to this line, an error occured that

Traceback (most recent call last):
  File "seq2seq-translation-batched.py", line 83, in <module>
    from masked_cross_entropy import *
ImportError: No module named masked_cross_entropy

But import torch seems fine.
And my PyTorch version is

>>> torch.__version__

What can I do? I’ve not found any thing about this import issue.

from masked_cross_entropy import * implies you have a file called masked_cross_entropy in the same directory as your ipynb. Is this true?

Thank you!
I’ve found the mistake.
I forgot to add this file into the same folder of my script.