python自定义类并使用的方法

class Person:
  def __init__(self, first, middle, last, age):
   self.first = first;
   self.middle = middle;
   self.last = last;
   self.age = age;
  def __str__(self):
   return self.first + ' ' + self.middle + ' ' + self.last +     ' ' + str(self.age)
  def initials(self):
   return self.first[0] + self.middle[0] + self.last[0]
  def changeAge(self, val):
   self.age += val
myPerson = Person('Raja', 'I', 'Kumar', 21)
print(myPerson)
myPerson.changeAge(5)
print(myPerson)
print(myPerson.initials())

Raja I Kumar 21
Raja I Kumar 26
RIK