[Python-ideas] Expose a child factory using MappingProxyType in builtins

We have the immutable frozenset for sets and and tuples for lists. But we also have something to manipulate dict as immutable datastructures:

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from types import MappingProxyType as idict d = idict({'a':1, 'b':2, 'c':3}) d['a'] = 4 Traceback (most recent call last): File "<ipython-input-3-c6f93d6278af>", line 1, in <module> d['a'] = 4 TypeError: 'mappingproxy' object does not support item assignment

We could expose this as a built type to allow the last of the most important data structure in Python to be easily immutable.