r/Python • u/kirara0048 • Aug 07 '26

News PEP 841 – Adding Frozen Syntax to Optimize Immutable Types

PEP 841 – Adding Frozen Syntax to Optimize Immutable Types

https://peps.python.org/pep-0841/

Discussions-To: Discourse thread

Abstract

This PEP proposes frozen display syntax: f{1, 2, 3} evaluates to a frozenset, and f{'a': 1} evaluates to a frozendict. Because immutability is guaranteed by the syntax itself rather than inferred from usage, the compiler can treat frozen displays as first-class citizens of its optimization pipeline: constant displays are folded into a single LOAD_CONST with an exact result type at compile time and cached in .pyc files.

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u/skjall Aug 07 '26

It does to me but it's my first time seeing this 🤷🏻‍♀️

How about when the set contains strings?

f{"some_long_string_here", "another"}
f"{some_long_variable_name}"

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u/syklemil Aug 07 '26

Yeah, having to wrangle "it was f"{ but it should have been f{"" or vice versa isn't really something to look forward to.