The best new features in Python 3.15

"Lazy imports allow imports to be processed only when they're actually used by the program. Thus for slow-importing modules that impose a large cost on a program's startup time, you can now easily defer that cost to when the code of that module will actually be executed. You can use lazy imports explicitly using the new lazy import syntax, but you can also force code with conventional imports to behave lazily, either programmatically or by using an environment variable. This makes it easy to make existing code take advantage of this feature without tons of rewriting. Best of all, there's no drawback to making imports lazy: they otherwise behave exactly as intended."

"The frozendict behaves like a regular dictionary, except that it's immutable (you can't add, remove, or change elements) and it's hashable (so you can use it as a key in another dictionary, for instance)."

"The new syntax ,sentinel("NAME") creates unique objects that compare only to themselves via the is operator. These objects can be type-checked properly, and they have an informative representation instead of just a random object descriptor."

"Highlights of Python 3.15, now available in beta, include lazy imports, faster JITs, better error messages, and smarter profiling."

Python 3.15 beta introduces lazy imports that delay importing modules until their code is actually used, reducing startup time for slow-importing modules. Lazy behavior can be enabled explicitly with new syntax or applied to conventional imports via programmatic control or an environment variable, without changing import semantics. A new frozendict built-in type provides an immutable, hashable dictionary usable as a key in other dictionaries. A new sentinel built-in type replaces the common object()-based sentinel pattern by creating unique objects that compare only to themselves with the is operator, support proper type checking, and provide informative representations. The release also includes faster JITs, better error messages, and a statistical sampling profiler.

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