René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Major slowdown on large listcomp","articleBody":"# Bug report\n\n### Bug description:\n\nThat started within the last 48 hours, on the main branch. Here's test code; it's possible it could be simplified\n\n```python\nif 1:\n    class Obj:\n        def __init__(self, i):\n            self.val = i\n\n    import sys\n    print(sys.version)\n    from time import perf_counter as now\n\n    start = now()\n    xs = [Obj(i) for i in range(2**21)]\n    finish = now()\n    print(finish - start)\n```\n\nUnder 3.12.2 it takes about a second, but under current main about 21 seconds.\n\n```none\nC:\\Code\\Python\\PCbuild\u003epy \\MyPy\\small.py\n3.12.2 (tags/v3.12.2:6abddd9, Feb  6 2024, 21:26:36) [MSC v.1937 64 bit (AMD64)]\n0.9562742999987677\n\nC:\\Code\\Python\\PCbuild\u003eamd64\\python.exe \\MyPy\\small.py\n3.13.0a5+ (heads/main:f4cc77d494, Mar 20 2024, 20:28:50) [MSC v.1939 64 bit (AMD64)]\n20.99507549998816\n```\n\nIf the size of the list is increased, it appears to suffer much worse than linear-time slowdown.\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nWindows\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-117120\n* gh-117213\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/tim-one","@type":"Person","name":"tim-one"},"datePublished":"2024-03-21T01:37:03.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/117108/cpython/issues/117108"}