PyCharm lets you compare the following via context menu commands:

• directories
• a class or class member with another class or class member
• a local file with its versions in Local History
• a local file with its current revision in your version control repository
• any two revisions of the same file
• any local file with the file currently opened in the Editor
• any two local files with each other: text or binary
• active Editor with the clipboard contents
• any text sources you paste into a blank diff window

You can configure the Diff tool in the Settings/Preferences dialog &shortcut:ShowSettings; under Tools | Diff & Merge.