René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"argparse performance regression in 3.14+ due to colorization overhead","articleBody":"I spent some time running the [argparse `bm_subparsers` benchmark](https://github.com/python/pyperformance/blob/e9fab3a7fc636376dbd150038079cf6039a4ab3f/pyperformance/data-files/benchmarks/bm_argparse/run_benchmark.py#L86) from `pyperformance` (1000 optional arguments, 10 iterations)\n\n| Version | Time | Function Calls |\n|---------|------|----------------|\n| 3.10 | 0.585s | 560K |\n| 3.11 | 0.207s | 560K |\n| 3.12 | 0.229s | 560K |\n| 3.13 | 0.246s | 560K |\n| **3.14** | **0.934s** | **2,380K** |\n| **3.15 (main)** | **0.883s** | **2,367K** |\n\nFor a \"realistic\" CLI with 10 arguments, parser creation is ~3x slower on main compared to 3.13.\n\nThe root cause is that `_get_formatter()` is called twice per `add_argument()` - [once for metavar validation](https://github.com/python/cpython/blob/2dac9e6016c81abbefa4256253ff5c59b29378a7/Lib/argparse.py#L1573) and once in [`_check_help()`](https://github.com/python/cpython/blob/2dac9e6016c81abbefa4256253ff5c59b29378a7/Lib/argparse.py#L1769) for help string validation (called at [the end of `add_argument`](https://github.com/python/cpython/blob/2dac9e6016c81abbefa4256253ff5c59b29378a7/Lib/argparse.py#L1579) ). Each `_get_formatter()` call creates a new `HelpFormatter`, which calls `_set_color()`, which calls `can_colorize()`, which checks 5 environment variables. \n\nI think a viable fix is to cache the `HelpFormatter` on `ArgumentParser` for validation operations. The validation only performs read-only operations (`_format_args`, `_expand_help`) that don't modify formatter state. This preserves the existing `_get_formatter()` behavior while eliminating redundant `_set_color()` calls during argument setup.\n\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-142268\n* gh-142313\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/savannahostrowski","@type":"Person","name":"savannahostrowski"},"datePublished":"2025-12-04T19:37:48.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/142267/cpython/issues/142267"}