Python 3.15 ships lazy imports, Tachyon sampling profiler as 3.10 hits end of life

Simon Willison · rss · 2026-10-13

Simon Willison rounds up Python 3.15's release highlights now that 3.10 is unsupported.

PEP 810 explicit lazy imports (lazy import ) defer loading until first use — a direct fix for plugin startup costs from heavy deps like sentencetransformers.
PEP 798 unpacking in comprehensions: [L for L in lists] flattens lists, sets, and dicts.
A new stdlib sampling profiler, Tachyon (profiling.sampling), can attach to running processes by PID and produce flame graphs, heat maps, and Firefox-profiler-compatible output.
Performance is roughly on par with 3.14, but the experimental JIT showed its first meaningful gain (1.2x on a Fibonacci benchmark).
He shares his exact uv commands to upgrade and pins 3.15 globally, then unlocks 3.11 features like TaskGroup, tomllib, datetime.UTC, and SQLite improvements.

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