python 笔记

##笔记
# 成员访问
# 基本的序列和映射规则

__len__(self)__
getitem__(self, key)__
setitem__(self, key, value)__
delitem__(self, key)

class X():
    pass

##>>> len(X())
##Traceback (most recent call last):
##  File "<stdin>", line 1, in <module>
##TypeError: object of type 'X' has no len()


class B():
    def __init__(self):
        pass
    def __len__(self):  #  implement the len()
        return 10

##>>> len(B())
##10

# 属性
class Rect():
    def __init__(self):
        self.width = 0
        self.height = 0
    def setSize(self, size):        # size 为 tuple
        self.width, self.height = size
    def getSize(self):
        return self.width, self,height
r = Rect()
r.setSize((100, 150))
r.getSize()

# property 函数

    
class Rect():
    def __init__(self):
        self.width = 0
        self.height = 0
    def setSize(self, size):        # size 为 tuple
        self.width, self.height = size
    def getSize(self):
        return self.width, self,height

    size = property(getSize, setSize)  # 此行

r = Rect()
r.width = 10
r.height = 5
r.size
>>>(10, 5)
>>>r.size = 150, 100
>>>r.width
150

# 这是一个很怪异的东西，虽然很怪异，但是在新式类中非常重要
# 静态方法和类成员方法

__metaclass__ = type
class MyClass():
    def smeth():
        print 'this is a static method'
    smeth = staticmethod(smeth)
    def cmeth(cls):
        print 'this is a class method of .' ,cls
    cmeth = classmethod(cmeth)

##>>> MyClass.smeth()
##this is a static method
##>>> MyClass().cmeth()
##this is a class method of . <class '__main__.MyClass'>
##>>> MyClass.cmeth()
##this is a class method of . <class '__main__.MyClass'>
##>>> MyClass.smeth()
##this is a static method
##>>>

# 采用修饰器的方式

__metaclass = type
class MyClass:
    @staticmethod       # 修饰器
    def smeth():
        print 'this is a static method'
    @classmethod
    def cmeth(cls):
        print 'this is a class method of .' cls

# __getattr__ setattt__ 和 他的朋友们

__getattribute__(self, name)
__getattr__(self, name)
__setattr__(self, name, value)
__delattr__(self, name)

class Rect:
    def __init__(self):
        self.width = 0
        self.height = 0
    def __setattr__(self, name, value):
        if name == 'size':
            self.width, self.height = value
        else:
            self.__dict__[name] = value
    def __getattr__(self, name):
        if name == 'size':
            return self.width, self.height
        else:
            raise AttributeError

# 迭代器 __iter__

# __iter__ 方法返回一个迭代器（iterator），所谓的迭代器就是具有 next() 方法的对象，这个方法在调用时不需要任何参数，在
# 调用next方法时，迭代器会返回它的下一个值。如果next方法被调用，但迭代器没有值可以返回，就会引发一个StopIteration异常
# 3.0中发生了一些变化

class Fibs:
    def __init__(self):
        self.a = 0
        self.b = 1
    def next(self):
        self.a, self.b = self.b, self.a + self.b
        return self.a
    def __iter__(self):
        return self

# 一个实现了 __iter__ 方法的对象是可以迭代的，一个实现了next方法的对象则是迭代器
fibs = Fibs()
for f in fibs:
    if f>1000:
        print(f)
        break


# 内建函数iter可以从可迭代的对象中获得迭代器
##it = iter([1,2,3])
##>>>it.next()
##1
##>>>it.next()
##2

# 从迭代器得到序列
class TestIterator:
    value = 0
    def next(self):
        self.value += 1
        if self.value > 10 :raise StopIteration
        return self.value
    def __iter__(self):
        return self

##>>> ti = TestIterator()
##>>> list(ti)
##[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
##>>>

# 生成器 yield
l = [[1,3,4], [5,7,9], [12,4,5]]
def flatten(nested):
    for sublist in nested:
        for element in sublist:
            yield element

##>>> flatten(l)
##<generator object flatten at 0x01AD1148>
##>>> list(flatten(l))
##[1, 3, 4, 5, 7, 9, 12, 4, 5]
##>>>

# 循环生成器 列表推到
g = ((i+2)**2 for i in range(2, 27))
g.next()
16

# 递归生成器

def flatten(nested):
    try:
        for sublist in nested:
            for element in flatten(sublist):
                yield element
    except TypeError:
        yield nested

# 改进版

def flatten(nested):
    try:
        try:nested + ''
        except TypeError: pass
        else: raise TypeError
        for sublist in nested:
            for element in flatten(sublist):
                yield element
    except TypeError:
        yield nested

l = [['foo'],['abc'], ['def']]
for x in flatten(l):
    print x



# 生成器方法 send
# 使用send方法，只有在生成器挂起之后才有意义，也就是说yield函数第一次被执行以后

def repeater(value):
    while True:
        new = (yield value)
        if new is not None : value = new
##>>> r = repeater(38)
##>>> r.next()
##38
##>>> r.send('Hello Python')
##'Hello Python'
##>>>

# throw close 方法 自行查阅
# 模拟生成器
def flatten(nested):
    result = []
    try:
        try: nested + ''
        except TypeError:pass
        else: raise TypeError
        for sublist in nested:
            for element in flatten(sublist):
                result.append(element)
    except TypeError:
         result.append(nested)
    return result