[Python-Dev] PEP 416: Add a frozendict builtin type (original) (raw)

Victor Stinner victor.stinner at haypocalc.com
Thu Mar 1 13:23:26 CET 2012

Rationale =========

A frozendict mapping cannot be changed, but its values can be mutable (not hashable). A frozendict is hashable and so immutable if all values are hashable (immutable). The wording of the above seems very unclear to me. Do you mean "A frozendict has a constant set of keys, and for every key, d[key] has a specific value for the lifetime of the frozendict. However, these values may be mutable. The frozendict is hashable iff all of the values are hashable." ? (or somesuch)

New try:

"A frozendict is a read-only mapping: a key cannot be added nor removed, and a key is always mapped to the same value. However, frozendict values can be mutable (not hashable). A frozendict is hashable and so immutable if and only if all values are hashable (immutable)."

* Register frozendict has a collections.abc.Mapping s/has/as/ ?

Oops, fixed.

If frozendict is used to harden Python (security purpose), it must be implemented in C. A type implemented in C is also faster. You mention security purposes here, but this isn't mentioned in the Rationale or Use Cases

I added two use cases: security sandbox and cache.

Hope this is helpful

Yes, thanks.

Victor

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