爲什麼__getattr__函數不起作用？

Question

我有個小類我寫了嘗試與定製__getattr__方法打球，我每次運行它的時候，我得到一個屬性錯誤：

class test: 
    def __init__(self): 
     self.attrs ={'attr':'hello'} 
    def __getattr__(self, name): 
     if name in self.attrs: 
      return self.attrs[name] 
     else: 
      raise AttributeError 

t = test() 
print test.attr 

的輸出是：

Traceback (most recent call last): 
    File "test.py", line 11, in <module> 
    print test.attr 
AttributeError: class test has no attribute 'attr' 

什麼給了？我認爲getattr之前調用屬性錯誤？

Answer 1

因爲類test不有attr作爲屬性，實例t有：

class test: 
    def __init__(self): 
     self.attrs ={'attr':'hello'} 
    def __getattr__(self, name): 
     if name in self.attrs: 
      return self.attrs[name] 
     else: 
      raise AttributeError 

t = test() 
print t.attr 

Answer 2

你要查詢的屬性上實例（t），而不是在類（test）：

>>> t = test() 
>>> print t.attr 
hello