Refactoring same code across 2 classes in python

I have two classes with similar first checking codes, but different behaviors. I supose there is a way to refactor the code, so I dont need to retype it every time. It is possible to refactor this, or I must retype this code everytime?

# Get actual logged user
user, msg = checkLoggedUser()
if user:
    self.renderPage("customMessage.htm", custom_msg=msg)
else:

The code is simple. Forget about my way to render the page, is a method over my own PageHandler class that works

# Check for actual logged user
def checkLoggedUser():
    # Get actual logged user
    user = users.get_current_user()

    # Don't allow to register for a logged user
    if user:
        return True, "You are already logged in."
    else:
        return False, None

# Get and post for the login page
class Login(custom.PageHandler):
    def get(self):
        # Get actual logged user
        user, msg = checkLoggedUser()
        if user:
            self.renderPage("customMessage.htm", custom_msg=msg)
        else:
            self.renderPage('login.htm')

    def post(self):
        # Get actual logged user
        user, msg = checkLoggedUser()
        if user:
            self.renderPage("customMessage.htm", custom_msg=msg)
        else:
            # Make the login
            # bla, bla bla... code for login the user.

# Get and post for the register page
class Register(custom.PageHandler):
    def get(self):
        # Get actual logged user
        user, msg = checkLoggedUser()
        if user:
            self.renderPage("customMessage.htm", custom_msg=msg)
        else:
            self.renderPage("registerUser.htm")

    def post(self):
        # Get actual logged user
        user, msg = checkLoggedUser()
        if user:
            self.renderPage("customMessage.htm", custom_msg=msg)
        else:
            # Store in vars the form values
            # bla, bla bla... code for register the user.