Question

我有以下类用于存储其他对象访问的设置：

#!/usr/bin/env python                                                           

class Settings:                                                                    
    """Singleton settings class"""                                              

    settings = {                                                                   
                   'SectionA': {'a': 1, 'b': 2, 'c': 3},                           
                   'SectionB': {'d': 4, 'e': 5, 'f': 6}                            
               }                                                                   

    def __getitem__(self, key): return self.settings[key]                          
    def __setitem__(self, key, item): self.settings[key] = item                    
    def keys(self): return self.settings.keys()                                    

s = Settings()                                                                     
print s.keys()                                                                     
print s['SectionA']                                                                
print s['SectionB']                                                                

for key in s: print s[key]

我无法理解为什么它会产生以下输出或如何绕过它，任何帮助都非常感激：

foo@bar:~$ python Settings.py
['SectionB', 'SectionA']
{'a': 1, 'c': 3, 'b': 2}
{'e': 5, 'd': 4, 'f': 6}
Traceback (most recent call last):
  File "Settings.py", line 20, in <module>
    for key in s: print s
  File "Settings.py", line 11, in __getitem__
    def __getitem__(self, key): return self.settings[key]
KeyError: 0
foo@bar:~$

Answer 1

那是因为当你在Settings类上进行迭代时，它显然会尝试通过索引迭代它，就像列表一样。第一个索引是0，它给出了一个KeyError，因为它不在你的dict中。您必须定义特殊方法来覆盖for key in s语法以迭代密钥。

def __iter__(self): return iter(self.settings)

编辑：另一件事是您正在使用已弃用的旧样式类。您应该将其更改为Settings(object)

Answer 2

这有效：

class Settings(dict):                                                                    
    """Singleton settings class"""                                              

    settings = {                                                                   
                   'SectionA': {'a': 1, 'b': 2, 'c': 3},                           
                   'SectionB': {'d': 4, 'e': 5, 'f': 6}                            
               }                                                                   

    def __getitem__(self, key): return self.settings[key]                          
    def __setitem__(self, key, item): self.settings[key] = item                    
    def keys(self): return self.settings.keys()                                    

s = Settings()                                                                     

for key in s.keys(): 
    print key 
    print s[key]

打印：

SectionB
{'e': 5, 'd': 4, 'f': 6}
SectionA
{'a': 1, 'c': 3, 'b': 2}

修改

看看，没有{}.keys()：

class Settings(dict): """Singleton settings class""" settings = { 'SectionA': {'a': 1, 'b': 2, 'c': 3}, 'SectionB': {'d': 4, 'e': 5, 'f': 6} } def __getitem__(self, key): return self.settings[key] def __setitem__(self, key, item): self.settings[key] = item def __iter__(self): return iter(self.settings.keys()) def keys(self): return self.settings.keys() s = Settings() for key in s: print key print s[key]

打印相同的输出......

Python字典类，'KeyError'

2 个答案: