Python学习笔记2016/1/20

Python学习笔记

# 定制类    
# ① __str__  ②  __repr__()
class Student(object):
    def __init__(self,name):
        self.name = name
    def __str__(self):
        return 'Student object (name:%s)' % self.name
    __repr__ = __str__

print(Student('pengyao'))
# Student object (name:pengyao) 有__str__的输出
# <__main__.Student object at 0x109afb190>  没有__str__的输出

# ③  __iter__ 以菲波那切数列数列为例
class Fib(object):
    def __init__(self):
        self.a,self.b = 0,1
    def __iter__(self):
        return self
    def __next__(self):
        self.a,self.b = self.b,self.a+self.b
        if(self.a > 100):
            raise StopIteration()
        return self.a

# Fib()即Fib类的实例，实例化过程就包含了循环过程
print(list(Fib()))
# 输出：[1,1,2,3,5,8,13,21,34,55,89]

# 把Fib实例作用于for循环
for n in Fib():
    print(n)

# ④ __getitem__
# Fib实例虽然能作用于for循环，看起来和list有点像，
# 但是，把它当成list来使用还是不行，比如，取第5个元素：
# print(Fib()[5])  #TypeError: 'Fib' object does not support indexing
# 要表现得像list那样按照下标取出元素，需要实现__getitem__()方法
class Fib4(object):
    def __getitem__(self,n):
        a,b = 1,1
        for x in range(n):
            a,b = b,a+b
        return a
f = Fib4()
print(f[3]) # 3