Why is a class __dict__ a mappingproxy?

Question

I wonder why a class __dict__ is a mappingproxy, but an instance __dict__ is just a plain dict

>>&g         


        

Answer 1

A mappingproxy is simply a dict with no __setattr__ method.

You can check out and refer to this code.

from types import MappingProxyType
d={'key': "value"}
m = MappingProxyType(d)
print(type(m)) # 

m['key']='new' #TypeError: 'mappingproxy' object does not support item assignment

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mappingproxy is since Python 3.3. The following code shows dict types:

class C:pass
ci=C()
print(type(C.__dict__)) #
print(type(ci.__dict__)) #