不可变得字典类型

>>> from types import MappingProxyType
>>> d = {'name':'zhangsan'}
>>> d_proxy = MappingProxyType(d)  # 返回一个只读视图
>>> d_proxy
mappingproxy({'name': 'zhangsan'})
>>> d_proxy['name']
'zhangsan'
>>> d_proxy['age'] =  18   # 不能修改
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'mappingproxy' object does not support item assignment
>>> d['age'] = 18  # 修改原映射
>>>
>>> d_proxy   # 在只读视图上反映出原映射做了修改
mappingproxy({'name': 'zhangsan', 'age': 18})

类对象的属性为一个不可变映射

>>> ll = []
>>> ll.__class__.__dict__
mappingproxy({'__new__': <built-in method __new__ of type object at 0x00007FFD648B6610>, '__repr__': <slot wrapper '__repr__' of 'list' objects>, '__hash__': None, '__getattribute__': <slot wrapper '__getattribute__' of 'list' objects>, '__lt__': <slot wrapper '__lt__' of 'list' objects>, '__le__': <slot wrapper '__le__' of 'list' objects>, '__eq__': <slot wrapper '__eq__' of 'list' objects>, '__ne__': <slot wrapper '__ne__' of 'list' objects>, '__gt__': <slot wrapper '__gt__' of 'list' objects>, '__ge__': <slot wrapper '__ge__' of 'list' objects>, '__iter__': <slot wrapper '__iter__' of 'list' objects>, '__init__': <slot wrapper '__init__' of 'list' objects>, '__len__': <slot wrapper '__len__' of 'list' objects>, '__getitem__': <method '__getitem__' of 'list' objects>, '__setitem__': <slot wrapper '__setitem__' of 'list' objects>, '__delitem__': <slot wrapper '__delitem__' of 'list' objects>, '__add__': <slot wrapper '__add__' of 'list' objects>, '__mul__': <slot wrapper '__mul__' of 'list' objects>, '__rmul__': <slot wrapper '__rmul__' of 'list' objects>, '__contains__': <slot wrapper '__contains__' of 'list' objects>, '__iadd__': <slot wrapper '__iadd__' of 'list' objects>, '__imul__': <slot wrapper '__imul__' of 'list' objects>, '__reversed__': <method '__reversed__' of 'list' objects>, '__sizeof__': <method '__sizeof__' of 'list' objects>, 'clear': <method 'clear' of 'list' objects>, 'copy': <method 'copy' of 'list' objects>, 'append': <method 'append' of 'list' objects>, 'insert': <method 'insert' of 'list' objects>, 'extend': <method 'extend' of 'list' objects>, 'pop': <method 'pop' of 'list' objects>, 'remove': <method 'remove' of 'list' objects>, 'index': <method 'index' of 'list' objects>, 'count': <method 'count' of 'list' objects>, 'reverse': <method 'reverse' of 'list' objects>, 'sort': <method 'sort' of 'list' objects>, '__class_getitem__': <method '__class_getitem__' of 'list' objects>, '__doc__': 'Built-in mutable sequence.\n\nIf no argument is given, the constructor creates a new empty list.\nThe argument must be an iterable if specified.'})
>>>