我如何使Python字典成员访问通过点“。”?

例如,我想写mydict.val而不是mydict['val']。

我还想以这种方式访问嵌套字典。例如

mydict.mydict2.val 

会提到

mydict = { 'mydict2': { 'val': ... } }

当前回答

基于Kugel的回答,并考虑到Mike Graham的警告,如果我们制作一个包装器呢?

class DictWrap(object):
  """ Wrap an existing dict, or create a new one, and access with either dot 
    notation or key lookup.

    The attribute _data is reserved and stores the underlying dictionary.
    When using the += operator with create=True, the empty nested dict is 
    replaced with the operand, effectively creating a default dictionary
    of mixed types.

    args:
      d({}): Existing dict to wrap, an empty dict is created by default
      create(True): Create an empty, nested dict instead of raising a KeyError

    example:
      >>>dw = DictWrap({'pp':3})
      >>>dw.a.b += 2
      >>>dw.a.b += 2
      >>>dw.a['c'] += 'Hello'
      >>>dw.a['c'] += ' World'
      >>>dw.a.d
      >>>print dw._data
      {'a': {'c': 'Hello World', 'b': 4, 'd': {}}, 'pp': 3}

  """

  def __init__(self, d=None, create=True):
    if d is None:
      d = {}
    supr = super(DictWrap, self)  
    supr.__setattr__('_data', d)
    supr.__setattr__('__create', create)

  def __getattr__(self, name):
    try:
      value = self._data[name]
    except KeyError:
      if not super(DictWrap, self).__getattribute__('__create'):
        raise
      value = {}
      self._data[name] = value

    if hasattr(value, 'items'):
      create = super(DictWrap, self).__getattribute__('__create')
      return DictWrap(value, create)
    return value

  def __setattr__(self, name, value):
    self._data[name] = value  

  def __getitem__(self, key):
    try:
      value = self._data[key]
    except KeyError:
      if not super(DictWrap, self).__getattribute__('__create'):
        raise
      value = {}
      self._data[key] = value

    if hasattr(value, 'items'):
      create = super(DictWrap, self).__getattribute__('__create')
      return DictWrap(value, create)
    return value

  def __setitem__(self, key, value):
    self._data[key] = value

  def __iadd__(self, other):
    if self._data:
      raise TypeError("A Nested dict will only be replaced if it's empty")
    else:
      return other

其他回答

您可以使用SimpleNamespace来实现这一点

from types import SimpleNamespace
# Assign values
args = SimpleNamespace()
args.username = 'admin'

# Retrive values
print(args.username)  # output: admin

使用namedtuple允许点访问。

它就像一个轻量级对象,也具有元组的属性。

它允许定义属性并使用点操作符访问它们。

from collections import namedtuple
Data = namedtuple('Data', ['key1', 'key2'])

dataObj = Data(val1, key2=val2) # can instantiate using keyword arguments and positional arguments

使用点运算符访问

dataObj.key1 # Gives val1
datObj.key2 # Gives val2

使用元组索引进行访问

dataObj[0] # Gives val1
dataObj[1] # Gives val2

但记住这是一个元组;不是字典。因此下面的代码将给出错误

dataObj['key1'] # Gives TypeError: tuple indices must be integers or slices, not str

参考:namedtuple

不喜欢。在Python中,属性访问和索引是分开的事情,您不应该希望它们执行相同的操作。创建一个类(可能是由namedtuple创建的),如果你有一些应该具有可访问属性的东西,并使用[]符号从字典中获取一个项。

使用SimpleNamespace:

>>> from types import SimpleNamespace   
>>> d = dict(x=[1, 2], y=['a', 'b'])
>>> ns = SimpleNamespace(**d)
>>> ns.x
[1, 2]
>>> ns
namespace(x=[1, 2], y=['a', 'b'])

这是我对@derek73的回答。我用字典。__getitem__作为__getattr__,因此它仍然抛出KeyError,并且im重命名字典公共方法以“”前缀(“”包围导致特殊方法名称冲突,如__get__将被视为一个描述符方法)。无论如何,由于关键的dict基方法,您无法将键作为属性获得完全清晰的命名空间,因此解决方案并不完美,但您可以拥有键属性,如get, pop, items等。

class DotDictMeta(type):                                                          
    def __new__(                                                                  
        cls,                                                                      
        name,                                                                     
        bases,                                                                    
        attrs,                                         
        rename_method=lambda n: f'__{n}__',                            
        **custom_methods,                                                         
    ):                                                                            
        d = dict                                                                  
        attrs.update(                                                             
            cls.get_hidden_or_renamed_methods(rename_method),           
            __getattr__=d.__getitem__,                                            
            __setattr__=d.__setitem__,                                            
            __delattr__=d.__delitem__,                                            
            **custom_methods,                                                     
        )                                                                         
        return super().__new__(cls, name, bases, attrs)                           
                                                                                  
    def __init__(self, name, bases, attrs, **_):                                  
        super().__init__(name, bases, attrs)                                      
                                                                                  
    @property                                                                     
    def attribute_error(self):                                                    
        raise AttributeError                                                      
                                                                                  
    @classmethod                                                                  
    def get_hidden_or_renamed_methods(cls, rename_method=None):                  
        public_methods = tuple(                                                   
            i for i in dict.__dict__.items() if not i[0].startswith('__')         
        )                                                                         
        error = cls.attribute_error                                               
        hidden_methods = ((k, error) for k, v in public_methods)                  
        yield from hidden_methods                                                 
        if rename_method:                                                       
            renamed_methods = ((rename_method(k), v) for k, v in public_methods) 
            yield from renamed_methods                                             
                                                                                  
                                                                                  
class DotDict(dict, metaclass=DotDictMeta):                                       
    pass  

                                                                    
                                                                              

你可以从DotDict命名空间中删除dict方法,并继续使用dict类方法,当你想操作其他dict实例并希望使用相同的方法而不需要额外检查它是否为DotDict时,它也很有用。

dct = dict(a=1)
dot_dct = DotDict(b=2)
foo = {c: i for i, c in enumerate('xyz')}
for d in (dct, dot_dct):
    # you would have to use dct.update and dot_dct.__update methods
    dict.update(d, foo)
    
assert dict.get(dot, 'foo', 0) is 0