浅析Python中的getattr(),setattr(),delattr(),hasattr()

getattr()函数是Python自省的核心函数，具体使用大体如下：

获取对象引用getattr

Getattr用于返回一个对象属性，或者方法

class A: 
def __init__(self): 
self.name = 'zhangjing' 
　　 #self.age=''
def method(self): 
print"method print" 
Instance = A() 
print getattr(Instance , 'name, 'not find') #如果Instance 对象中有属性name则打印self.name的值，否则打印'not find'
print getattr(Instance , 'age', 'not find') #如果Instance 对象中有属性age则打印self.age的值，否则打印'not find'
print getattr(a, 'method', 'default') 
#如果有方法method，否则打印其地址，否则打印default 
print getattr(a, 'method', 'default')() 
#如果有方法method，运行函数并打印None否则打印default 

注：使用getattr可以轻松实现工厂模式。

例：一个模块支持html、text、xml等格式的打印，根据传入的formate参数的不同，调用不同的函数实现几种格式的输出

import statsout 
def output(data, format="text"): 
output_function = getattr(statsout, "output_%s" % format) 
return output_function(data) 
setattr(object, name, value)
This is the counterpart of getattr(). The arguments
are an object, a string and an arbitrary value. The string may name an existing
attribute or a new attribute. The function assigns the value to the attribute,
provided the object allows it. For example, setattr(x,
'foobar', 123) is equivalent to
x.foobar = 123.

这是相对应的getattr()。参数是一个对象,一个字符串和一个任意值。字符串可能会列出一个现有的属性或一个新的属性。这个函数将值赋给属性的。该对象允许它提供。例如,setattr(x,“foobar”,123)相当于x.foobar = 123。

delattr(object, name)

This is a relative of setattr(). The arguments are
an object and a string. The string must be the name of one of the object's
attributes. The function deletes the named attribute, provided the object allows
it. For example, delattr(x, 'foobar') is
equivalent to del x.foobar.

与setattr()相关的一组函数。参数是由一个对象(记住python中一切皆是对象)和一个字符串组成的。string参数必须是对象属性名之一。该函数删除该obj的一个由string指定的属性。delattr(x, 'foobar')=del x.foobar

•hasattr用于确定一个对象是否具有某个属性。

语法：

hasattr(object, name) -> bool

判断object中是否有name属性，返回一个布尔值。

>>> li=["zhangjing","zhangwei"]
>>> getattr(li,"pop")
<built-in method pop of list object at 0x011DF6C0>
>>> li.pop
<built-in method pop of list object at 0x011DF6C0>
>>> li.pop()
'zhangwei'
>>> getattr(li,"pop")()
'zhangjing'
>>>getattr(li, "append")("Moe") 

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