>>> sys.path ['/private/var/mobile/Containers/Shared/AppGroup/C534C622-2FDA-41F7-AE91-E3AAFE5FFC6B/Pythonista3/Documents/site-packages-3', '/private/var/mobile/Containers/Shared/AppGroup/C534C622-2FDA-41F7-AE91-E3AAFE5FFC6B/Pythonista3/Documents/site-packages', '/var/containers/Bundle/Application/DBC1896E-6227-4695-9B4B-AC1340AD4945/Pythonista3.app/Frameworks/Py3Kit.framework/pylib', '/var/containers/Bundle/Application/DBC1896E-6227-4695-9B4B-AC1340AD4945/Pythonista3.app/Frameworks/Py3Kit.framework/pylib/site-packages', '/var/containers/Bundle/Application/DBC1896E-6227-4695-9B4B-AC1340AD4945/Pythonista3.app/Frameworks/Py3Kit.framework/pylib/site-packages/PIL_compat', '/var/containers/Bundle/Application/DBC1896E-6227-4695-9B4B-AC1340AD4945/Pythonista3.app/Frameworks/Py3Kit.framework/pylib/lib/python36.zip', '/var/containers/Bundle/Application/DBC1896E-6227-4695-9B4B-AC1340AD4945/Pythonista3.app/Frameworks/Py3Kit.framework/pylib/lib/python3.6', '/var/containers/Bundle/Application/DBC1896E-6227-4695-9B4B-AC1340AD4945/Pythonista3.app/Frameworks/Py3Kit.framework/pylib/lib/python3.6/lib-dynload']

which shows that site-packages-3 takes precedence over site-packages which takes precdence over the build in modules. (in the 2.7 interpreter, it uses site-packages-2 and site-packages) That is nice because you can update certain things, though you must also be careful you don't make a module with the same name as a builtin.

Some other info which might be useful, during startup, pythonista tries to import a module pythonista_startup which you could place in site-packages (applies to both interpreter) or site-packages-3. You could have your startup download weekly assignments or examples, print instructions, etc.