This is normal, if obscure, behaviour. Pythonw starts without a console, and so stdout is not connected to anything. As a result, you can't print (or pprint).

You'll need to set sys.stdout to something or provide a file if you want to print output.

If someone wants to contribute a specialised sys.stdout implementation that can raise a more helpful error message in this case, that would be helpful. But as it's a breaking change it would only go into 3.10.