After upgrade pycharm to 2018.1, and upgrade python to 3.6.5, pycharm reports "unresolved reference 'join'". The last version of pycharm doesn't show any warning for the line below:
from os.path import join, expanduser
May I know why?
(I used python 3.6.? before)
I tried almost everything I can find, such as delete and recreate interpreter, invalidate cache and restart, delete and recreate virtualenv... how do I fix this?
(I can run my program without any error.)
Sadly, it seems that PyCharm will try to evaluate the path to an existing file/folder, which in some cases will not exist and thus create this warning.
It's not very useful when you are building a path for something that's supposed to be created, because obviously it will not exist yet, but PyCharm will still complain.
You could try clicking on File > Invalidate Caches > Invalidate and Restart. This worked for me.
[edit] It will come back tho, not much else to do.
Check that pycharms is using the correct interpreter.
来源：https://stackoverflow.com/questions/49687860/pycharm-unresolved-reference-on-join-of-os-path