Indentation has tabs when only spaces are expected. Change all tabs to spaces.

Anti-pattern

Note: → represents a tab.

def get_name(self):
    if self.first_name and self.last_name:
    → → return self.first_name + ' ' + self.last_name
    else:
        return self.last_name

Best practice

Use spaces only.

def get_name(self):
    if self.first_name and self.last_name:
        return self.first_name + ' ' + self.last_name
    else:
        return self.last_name