Lesson3: lr_find() -> AttributeError: module '__main__' has no attribute '__spec__'

I just want to know whether lr_find() does a kind of memory validation before running. I’m runnungin Lesson 3 in my laptop and in the GPU (gradient cloud), the fact is in the GPU works fine but in my CPU it gives me the following error:

I know the difference between running in GPU and CPU. However, I was able to run Lesson1 and 2 in my laptop (despite it took ages). now since we create the databunch from the src it seems it does not work anymore on my CPU.

Is it the function or the installation of my fastai?
an help with this will be highly appreciated.