You can invoke UML class diagram from different places:
From the various tool windows.
From the Navigation bar.
From the Structure tool window.
From the editor.
PyCharm displays UML diagrams in two modes:
In a pop-up window.
In a separate editor tab.
To open a UML class diagram
Select the desired item, or open it in the editor.
Do one of the following:
On the context menu of the selection, click Diagram, and on the submenu, select the
way you want to view the model: Show Diagram or Show Diagram Pop-up.
Press Ctrl+Shift+Alt+UCtrl+Shift+Alt+U or Ctrl+Alt+UCtrl+Alt+U.