getattr
`getattr`函數屬于內建函數,可以通過函數名稱獲取
value = obj.attribute
value = getattr(obj, "attribute")
使用`getattr`來實現工廠模式
#一個模塊支持html、text、xml等格式的打印,根據傳入的formate參數的不同,調用不同的函數實現幾種格式的輸出
import statsout
def output(data, format="text"):??????????????????????????
??? output_function = getattr(statsout, "output_%s" %format)
??? return output_function(data)
__call__
`__call__`方法用于實例自身的調用:
class storage(dict):
??? # __call__方法用于實例自身的調用
??? #達到()調用的效果
??? def __call__ (self, key):
???????? try:
???????????? return self[key]
???????? except KeyError, k:
???????????? return None
s = storage()
s['key'] = 'value'
print s(key) #調用__call__
__getattr__
從對象中讀取某個屬性時,首先需要從self.__dicts__中搜索該屬性,再從__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 # 從__dict__里獲得的?
print a.age # 從__getattr__獲得的
__setattr__
`__setattr__`函數是用來設置對象的屬性,通過object中的__setattr__函數來設置屬性:
class A(object):
??? def __setattr__(self, *args, **kwargs):?
??????? print 'call func set attr'?
??????? return object.__setattr__(self, *args, **kwargs)
__delattr__
`__delattr__`函數式用來刪除對象的屬性:
class A(object):
??? def __delattr__(self, *args, **kwargs):?
??????? print 'call func del attr'?
??????? return object.__delattr__(self, *args, **kwargs)?
例子
完整例子可以參考微博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__函數實現_Executable函數對象為可調用的
??? 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對象,調用__init__函數
??????????? 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__
而在源碼中,存在下面代碼片段:
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,加入我們初始化對象,并調用某函數如下:
client = APIClient(...)
#會調用__getattr__函數,從而調用__call__函數
client.something.get()
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