9.2 构造方法
python 中也属于自己的构造函数和析构函数，
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
fib = fibs()
for i in fib:
if i>1000:
print i
break
其中的__init__ 就是在类创建对象的时候自动调用的，而下面两个函数就是在迭代的时候自动调用的，这是python实现的语法。
类在继承时不显示调用父类的构造方法时，父类构造方法中声明的元素不会被继承
class Bird:
def __init__(self):
self.hungry = True
def eat(self):
if self.hungry:
print ‘Ohhh.haha!‘
self.hungry = False
else:
print ‘I\‘m full Thanks!‘
class SongBird(Bird):
def __init__(self):
self.sound = ‘Squawk!‘
def sing(self):
print self.sound
b = Bird()
b.eat()
b.eat()
sb = SongBird()
sb.sing()
sb.eat()
>>>
Ohhh.haha!
I‘m full Thanks!
Squawk!
Traceback (most recent call last):
File "G:\New Knowledge\practice\python\test.py", line 21, in <module>
sb.eat()
File "G:\New Knowledge\practice\python\test.py", line 5, in eat
if self.hungry:
AttributeError: SongBird instance has no attribute ‘hungry‘
>>>
class Bird:
def __init__(self):
self.hungry = True
def eat(self):
if self.hungry:
print ‘Ohhh.haha!‘
self.hungry = False
else:
print ‘I\‘m full Thanks!‘
class SongBird(Bird):
def __init__(self):
self.sound = ‘Squawk!‘
Bird.__init__(self)
def sing(self):
print self.sound
b = Bird()
b.eat()
b.eat()
sb = SongBird()
sb.sing()
sb.eat()
>>> Ohhh.haha!
I‘m full Thanks!
Squawk!
Ohhh.haha!
>>>
# -*- coding: cp936 -*-
class Bird:
def __init__(self):
self.hungry = True
def eat(self):
if self.hungry:
print ‘Ohhh.haha!‘
self.hungry = False
else:
print ‘I\‘m full Thanks!‘
@classmethod
def say(self):
print ‘Hello ,everybody!‘
#类中的方法都至少带个self参数
#这样声明的函数只用类对象才能调用
#只有@classmethod 或@staticmethod 可用类名调用，而不需要生成实例对象
class SongBird(Bird):
def __init__(self):
self.sound = ‘Squawk!‘
Bird.__init__(self)
def sing(self):
print self.sound
b = Bird()
b.eat()
b.eat()
b.say()
Bird.say()
sb = SongBird()
sb.sing()
sb.eat()
>>>
Ohhh.haha!
I‘m full Thanks!
Hello ,everybody!
Hello ,everybody!
Squawk!
Ohhh.haha!
>>>
9.7递归生成器
# -*- coding: cp936 -*-
def flatten(nested):
try:
for sublist in nested:
for element in flatten(sublist):
yield element
except TypeError:
yield nested
def flatten_new(nested):
try:
try:nested + ‘‘#列表不能加字符
except:pass
else:raise TypeError
for sublist in nested:
for element in flatten_new(sublist):
yield element
except TypeError:
yield nested
test = [[[1],2],[3],[4,[5,[6,[7]]],8]]
test_char = [‘foo‘,[‘bar‘,[‘join‘]],‘tu‘]
print "old\n:",list(flatten(test))
print "new\n:",list(flatten_new(test))
print "new\n:",list(flatten_new(test_char))
print "old\n:",list(flatten(test_char))#死循环
old: [1, 2, 3, 4, 5, 6, 7, 8]
new
: [1, 2, 3, 4, 5, 6, 7, 8]
new
: [‘foo‘, ‘bar‘, ‘join‘, ‘tu‘]
old
:
Traceback (most recent call last):
File "G:/New Knowledge/practice/python/yield_test.py", line 24, in <module>
print "old\n:",list(flatten(test_char))
File "G:/New Knowledge/practice/python/yield_test.py", line 5, in flatten
for element in flatten(sublist):
File "G:/New Knowledge/practice/python/yield_test.py", line 5, in flatten
for element in flatten(sublist):
>>> def repeater(value):
while True:
new = (yield value)
if new is not None:value = new
>>> r = repeater(43)
>>> r.next()
43
>>> r.next()
43
>>> r.send("hello!")
‘hello!‘
>>> r.next()
‘hello!‘
>>>