[Python-ideas] Override dict.__new__ to raise if cls is not dict; do the same for str, list, etc.

[Chris Angelico]

On Thu, Apr 21, 2016 at 3:33 PM, Neil Girdhar <mistersheik at gmail.com> wrote:
>> Why should I inherit from UserDict instead? I have to import that from
>> somewhere (is it in types? collections? though presumably your error
>> message would tell me that), and then I have to contend with the fact
>> that my class is no longer a dictionary.
>
>
> Of course it's a dictionary.  It's an abc.Mapping, which is all a user of
> your class should care about.  After all, it "quacks like a duck", which is
> all that matters.

Your first sentence is in conflict with your other statements. My type
is simply *not* a dictionary. You can start raising bug reports all
over the place saying "JSON should look for abc.Mapping rather than
dict", but I'm not even sure that it should.

ChrisA