［Python进阶－5］类的特殊方法

（1）str和repr
——一般我们用print打印一个变量时，一般是调用了它的str方法。这里打印实例也是如此，调用了str，所以，我们可通过重写该方法获得我们想到的输入。
——但是如上的重写str只能在print x时有用，如果直接用x，输出的仍然是内存地址之类的，所以有另一个方法，就是repr这个其实是面向开发者的输出。也可以重新定义。

class Person(object):    def __init__(self, name, gender):        self.name = name        self.gender = genderclass Student(Person):    def __init__(self, name, gender, score):        super(Student, self).__init__(name, gender)        self.score = score    def __str__(self):        return '(Student:%s,%s,%s)'%(self.name,self.gender,self.score)    __repr__=__str__s = Student('Bob', 'male', 88)print s

（2）排序实现复习，按分数排序，分数相同则按名字

class Student(object):    def __init__(self, name, score):        self.name = name        self.score = score    def __str__(self):        return '(%s: %s)' % (self.name, self.score)    __repr__ = __str__    def __cmp__(self, s):        if self.score==s.score:            return cmp(self.name,s.name)        return -cmp(self.score,s.score)L = [Student('Tim', 99), Student('Bob', 88), Student('Alice', 99)]print sorted(L)＃[(Alice: 99), (Tim: 99), (Bob: 88)]

（3）联系str和len特殊方法

class Fib(object):    def __init__(self, num):        self.num=num        a,b,L=0,1,[]        for n in range(num):            L.append(a)            a,b=b,a+b        self.nums=L    def __str__(self):        return str(self.nums)    def __len__(self):        return self.numf = Fib(10)print fprint len(f)

（4）实现有理数的加减乘除

class Rational(object):    def __init__(self, p, q):        self.p = p        self.q = q    def __add__(self, r):        return Rational(self.p * r.q + self.q * r.p, self.q * r.q)    def __sub__(self, r):        return Rational(self.p * r.q - self.q * r.p, self.q * r.q)    def __mul__(self, r):        return Rational(self.p * r.p, self.q * r.q)    def __div__(self, r):        return Rational(self.p * r.q, self.q * r.p)    def __str__(self):        return '%s/%s'%(self.p,self.q)    __repr__ = __str__r1 = Rational(1, 2)r2 = Rational(1, 4)print r1 + r2print r1 - r2print r1 * r2print r1 / r2

（5）int和float实现类型转换

class Rational(object):    def __init__(self, p, q):        self.p = p        self.q = q    def __int__(self):        return self.p // self.q    def __float__(self):        return float(self.p)/self.qprint float(Rational(7, 2))print float(Rational(1, 3))

（6）利用@property可添加一个属性。也可以配套@属性.setter来设置属性值。

class Student(object):    def __init__(self, name, score):        self.name = name        self.__score = score    @property    def score(self):        return self.__score    @score.setter    def score(self, score):        if score < 0 or score > 100:            raise ValueError('invalid score')        self.__score = score    @property    def grade(self):        if self.score>=80:            return 'A'        elif self.score>=60:            return 'B'        else:            return 'C's = Student('Bob', 59)print s.grades.score = 60print s.grades.score = 99print s.grade

（7）slot固定了实例有的属性个数，不能随意添加

class Person(object):    __slots__ = ('name', 'gender')    def __init__(self, name, gender):        self.name = name        self.gender = genderclass Student(Person):    __slots__ = ('name','gender','score')    def __init__(self,name,gender,score):        super(Student,self).__init__(name,gender)        self.score=scores = Student('Bob', 'male', 59)s.name = 'Tim's.score = 99print s.score

（8）call，重写输出feb数列

class Fib(object):    def __call__(self,n):        a=0        b=1        L=[]        for x in range(n):            L.append(a)            a,b=b,a+b        return Lf = Fib()print f(10)