Say you would like to inherit the MailTrackingController from the OCA module mail_tracking. Here is how you do it.

I know that the mail_tracking module is not in the same directory as the odoo built-in addons. Still the below works(of course your module depends on the other module in the manifest file.)

# import importlib so as to use it
# to import the module that contains the
# controller we are to inherit
import importlib

# use importlib to import the module
# that contains the controller we need to inherit
mail_tracking = importlib.import_module('odoo.addons.mail_tracking')

# create the inheriting controller
class MailTrackingController(mail_tracking.
                                  controllers.main.
                                  MailTrackingController):

def mail_tracking_open(self, db, tracking_email_id, token=False, **kw):
    """
    Some doc sting
    """
    
    response = super(MailTrackingController, self).\
        mail_tracking_open(db, tracking_email_id, token, **kw)
    .
    .
    .