Please, see Soumith’s answer above:

  
    
    
    Got warning: Couldn't retrieve source code for container 
  
  
    I probably typed that answer out from my phone, which is why it was concise. 
Retrieving source code of a python class might happen for a variety of reasons, including: 

If you defined the class in the interpreter directly (like in ipython terminal / notebook, or python shell)
If you only have access to .pyc files but not the original .py files
If the class itself was auto-generated

The warning exists to let the user know that we cannot do some sanity checks upon loading the class back, which …
  


i.e. Jupyter env is just one of such possible situations.