day26

反射，四个方法，hasattr,getattr,setattr,delattr，一切皆对象
http://www.cnblogs.com/linhaifeng/articles/6204014.html

动态导入

#a 下的 test.py 文件
def test_a():
    print('this is a')

def _test_b():
    print('this is b')

（1）导入模块 from xxx import *

from a.test import *

test_a()
test_b()

输出结果：
#找不到 test_b 函数，就算改成_test_b 也是一样
NameError: name 'test_b' is not defined 
Process finished with exit code 1

（2）导入模块 __import__('a.test')

module_t = __import__('a.test') #传入字符串
print(module_t)  #定位到 test 文件的顶级目录 a
module_t.test.test_a()
module_t.test._test_b()  #私有函数也可调用

输出结果：
<module 'a' (namespace)>  # a 目录
this is a
this is b

（3）导入模块 importlib

import importlib

module_t = importlib.import_module('a.test')
print(module_t)  #直接定位到 test 
module_t.test_a()
module_t._test_b()

输出结果：
<module 'a.test' from 'C:\\Users\\libai\\PycharmProjects\\begin\\a\\test.py'> #a.test
this is a
this is b

__setattr__, __delattr__, __getattr__
实例化后增加，修改，获取属性时会触发 class 中的这些属性，具体可以看
http://www.cnblogs.com/linhaifeng/articles/6204014.html

class Earth:
    start = 0
    def __init__(self, name):
        self.name = name
    def __getattr__(self, item):
        print('this is getattr')

e = Earth('bbs')
print(e.name)
e.x  #获取一个不存在的属性，触发__getattr__

输出结果：
bbs
this is getattr

获取类的属性

class Earth:
    start = 0
    def __init__(self, name):
        self.name = name
    def __getattr__(self, item):
        print('this is getattr')

print(Earth.__dict__)  #获取的属性不完整
print(dir(Earth))   #获取所有的属性

输出结果：
{'__module__': '__main__', 'start': 0, '__init__': <function Earth.__init__ at 0x000001AE1FC64620>, '__getattr__': <function Earth.__getattr__ at 0x000001AE1FC646A8>, '__dict__': <attribute '__dict__' of 'Earth' objects>, '__weakref__': <attribute '__weakref__' of 'Earth' objects>, '__doc__': None}
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattr__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'start']

包装标准类型

class List(list):  #继承并修改 list 方法
    def show_list(self):
        for i in self:
            print(i, end='')
        print('')
    def append(self, object):
        print('append the', object)
        if type(object) == str:
            super(List, self).append(object) #调用父类
        else:
            print('only append str')
l = List('www.baidu.com')
l.show_list()
l.append(123)
l.append('www.google.com')
print(l)

输出结果：
www.baidu.com
append the 123
only append str
append the www.google.com
['w', 'w', 'w', '.', 'b', 'a', 'i', 'd', 'u', '.', 'c', 'o', 'm', 'www.google.com']

授权，也就是在 class 中调用类似于父类的方法和属性，但不继承于父类

import time
class open_file():
    def __init__(self, filename, mode='r', encoding='utf-8'):
        self.file = open(filename, mode, encoding=encoding) #直接调用 open 方法
        self.mode = mode
        self.encoding = encoding
    def write(self, item):
        print(item)
        t = time.strftime('%Y-%m-%d %X')
        self.file.write('%s %s' %(t, item)) #用实例的文件类 self.file 操作
    def read(self):
        print(self.file.read()[0:20]) #截出时间戳
    def __getattr__(self, item):
        print(item)
        return getattr(self.file, item) #返回属性调用

f = open_file('a.txt', 'w+', 'utf-8')
f.write('ni hao ma')
f.seek(0)
f.read()

输出结果：
ni hao ma
seek
2018-04-17 00:18:06