When I wrote the line with the caret shown on the snapshot below, the member "description" did not exist yet and I had the Documentation window open. As soon as I wrote the word "documentation" a "Fetching documentation" message started blinking on the documentation window and PyCharm started using 50% of my 8 core.
I created the "documentation" member, but nothing changed.
I closed and restarted PyCharm but nothing changed.
I opened another project and the CPU usage went down. Then I reopened this project and the CPU usage went up again.
I clicked on another line and the CPU usage went down. Then I clicked on that line again and the CPU usage went up again. The CPU usage is high when the caret is on the word "description" even if the focus is moved to another editor window.
The problem makes PyCharm almost unusable.
The workaround for me is easy: move the caret away from the word "description".
I made a copy of the whole folder. Please let me know if you want it to investigate the problem.
Anaconda with Python 3.6.4 - Pycharm 2017.3