I just installed the latest version of PyCharm (4.5).
Now I am experiencing unresolved reference errors. On the top of my code I have:
from datetime
As mentioned here try to delete the content of the skeleton folder. It reside inside of the settingsfolder (~/.PyCharmxxxx.xx/system/python_stubs) Removing/adding the python environment was not necessary for me. Simply restart PyCharm after removing the content (or the whole python_stubs folder)
This does the trick for me and now it works like a (py)charm again.
That's a known, already reported at https://youtrack.jetbrains.com/issue/PY-15460