[Python-Dev] Add a frozendict builtin type

[Victor Stinner]

>> A frozendict can be used as a member of a set or as a key in a dictionary.
>>
>> For example, frozendict is indirectly needed when you want to use an
>> object as a key of a dict, whereas one attribute of this object is a
>> dict.
>
> It isn't. You just have to define __hash__ correctly.

Define __hash__ on a mutable object can be surprising.

Or do you mean that you deny somehow the modification of the dict
attribute, and convert the dict to a immutable object before hashing
it?

>> frozendict helps also in threading and multiprocessing.
>
> How so?

For example, you don't need a lock to read the frozendict content,
because you cannot modify the content.

Victor