p1+p2出错，说p1未定义

Question

class Programer(object): def __init__(self, name, age): #super(Programer, self).__init__() #self.arg = arg self.name = name if isinstance(age,int): self.age = age def __eq__(self, other): if isinstance(other,Programer): if self.age == other.age: return True else: return False else: raise Exception('the type of object must be Programer') def __add__(self, other): if isinstance(other,Programer): return self.age + other.age else: raise Exception('the type of object must be Programer') if __name__=='__main__': p1 = Programer('Yue', 20) p2 = Programer('Wang', 24) print (p1 == p2) print (P1 + p2)结果：False    print (P1 + p2)NameError: name 'P1' is not defined