python encapsulation & information hiding demo

#quote from 'introduction to computation and programming using python, revised edition, MIT'
import datetime

class Person(object):
    
    def __init__(self, name):
        """Create a person"""
        self.name = name
        try:
            lastBlank = name.rindex(' ')
            self.lastName = name[lastBlank+1:]
        except:
            self.lastName = name
        self.birthday = None
        
    def getName(self):
        """Returns self's full name"""
        return self.name
        
    def getLastName(self):
        """Returns self's last name"""
        return self.lastName
        
    def setBirthday(self, birthdate):
        """Assumes bithdate is of type datetime.date
           Sets self's birthday to birthdate"""
        self.birthday = birthdate
        
    def getAge(self):
        """Returns self's current age in days"""
        if self.birthday == None:
            raise ValueError
        return (datetime.date.today() - self.birthday).days
        
    def __lt__(self, other):
        """Returns True if self's name is lexicographically
           less than other's name, and False otherwise"""
        if self.lastName == other.lastName:
            return self.name < other.name
        return self.lastName < other.lastName
        
    def __str__(self):
        """Returns self's name"""
        return self.name
        
class MITPerson(Person):
    
    nextIdNum = 0 #identification number, class variable
    
    def __init__(self, name):
        Person.__init__(self, name)
        self.idNum = MITPerson.nextIdNum
        MITPerson.nextIdNum += 1
        
    def getIdNum(self):
        return self.idNum
        
    def __lt__(self, other):
        return self.idNum < other.idNum
        
class Grades(object):
    """A mapping froms students to a list of grades"""
    def __init__(self):
        """Create empty grade book"""
        self.students = []
        self.grades = {}
        self.isSorted = True
        
    def addStudent(self, student):
        """Assumes: student is of type Student
           Add student to the grade book"""
        if student in self. students:
            raise ValueError('Duplicate student')
        self.students.append(student)
        self.grades[student.getIdNum()] = []
        self.isSorted = False
    
    def addGrade(self, student, grade):
        """Assumes: grade is a float
           Add grade to the list of grades for student"""
        try:
            self.grades[student.getIdNum()].append(grade)
        except:
            raise ValueError('Student not in mapping')
            
    def getGrade(self, student):
        """Return a list of grades for student"""
        try: #return copy of student's grades
            return self.grades[student.getIdNum()][:]
        except:
            raise ValueError('Student not in mapping')