Python __setattr__、 __getattr__、 __delattr__、__call__用法示例
投稿：junjie
getattr
`getattr`函数属于内建函数，可以通过函数名称获取
value = obj.attribute
value = getattr(obj, "attribute")
使用`getattr`来实现工厂模式
#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)
__call__
`__call__`方法用于实例自身的调用：
class storage(dict):
# __call__方法用于实例自身的调用
#达到()调用的效果
def __call__ (self, key):
try:
return self[key]
except KeyError, k:
return None
s = storage()
s['key'] = 'value'
print s(key) #调用__call__
__getattr__
从对象中读取某个属性时，首先需要从self.__dicts__中搜索该属性，再从__getattr__中查找。
class A(object):
def __init__(self):
self.name = 'from __dicts__: zdy'
def __getattr__(self, item):
if item == 'name':
return 'from __getattr__: zdy'
elif item == 'age':
return 26
a = A()
print a.name # 从__dict__里获得的
print a.age # 从__getattr__获得的
__setattr__
`__setattr__`函数是用来设置对象的属性，通过object中的__setattr__函数来设置属性：
class A(object):
def __setattr__(self, *args, **kwargs):
print 'call func set attr'
return object.__setattr__(self, *args, **kwargs)
__delattr__
`__delattr__`函数式用来删除对象的属性：
class A(object):
def __delattr__(self, *args, **kwargs):
print 'call func del attr'
return object.__delattr__(self, *args, **kwargs)
例子
完整例子可以参考微博API：http://github.liaoxuefeng.com/sinaweibopy/
class _Executable(object):
def __init__(self, client, method, path):
self._client = client
self._method = method
self._path = path
#__call__函数实现_Executable函数对象为可调用的
def __call__(self, **kw):
method = _METHOD_MAP[self._method]
if method==_HTTP_POST and 'pic' in kw:
method = _HTTP_UPLOAD
return _http_call('%s%s.json' % (self._client.api_url, self._path), method, self._client.access_token, **kw)
def __str__(self):
return '_Executable (%s %s)' % (self._method, self._path)
__repr__ = __str__
class _Callable(object):
def __init__(self, client, name):
self._client = client
self._name = name
def __getattr__(self, attr):
if attr=='get':
#初始化_Executable对象，调用__init__函数
return _Executable(self._client, 'GET', self._name)
if attr=='post':
return _Executable(self._client, 'POST', self._name)
name = '%s/%s' % (self._name, attr)
return _Callable(self._client, name)
def __str__(self):
return '_Callable (%s)' % self._name
__repr__ = __str__
而在源码中，存在下面代码片段：
class APIClient(object):
'''
API client using synchronized invocation.
'''
...
def __getattr__(self, attr):
if '__' in attr:
return getattr(self.get, attr)
return _Callable(self, attr)
因此，加入我们初始化对象，并调用某函数如下：
client = APIClient(...)
#会调用__getattr__函数，从而调用__call__函数
client.something.get()