PyCharm has a default keymap and even a nice PDF to show you all the most used commands when you navigate to Help | Default Keymap Reference (the same on Mac, Windows, and Linux).

On Mac, the default keymap is OSX 10.5+, and on both Windows and Linux, the default keymap is called Default. This can easily be changed by changing the keymap by going to Preferences (Mac) or Settings… (Windows/Linux).

Notice how my keymap is Mac OS X 10.5+ copy. This is because you cannot override a predefined configuration; you can only make your own copy of it. If my list is different from yours, it's because I imported some of my keymaps; in this case, Default copy from my Windows installation. Just like themes, you can import and export keymaps.