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compileall isn't reproducible #161434
Description
Bug report
If you repeatedly run python3 -mcompileall -f over the standard library, the generated .pyc files are not reproducible. I'm explicitly using the hash-based invalidation mode to avoid time stamps.
My reproducer is a copy of stdlib put into a git repo, then I delete .pyc files and regenerate them in a loop with:
$ python3 -mcompileall --invalidation-mode checked-hash pystdlib -f
With some repeating, and especially when using -j, I get different files. Interestingly, it's often the same files that change...
For example:
diff --git i/__pycache__/functools.cpython-314.pyc w/__pycache__/functools.cpython-314.pyc
index 506a7ba..ec11d46 100644
--- i/__pycache__/functools.cpython-314.pyc
+++ w/__pycache__/functools.cpython-314.pyc
@@ -441,12 +441,12 @@
00001b80 52 05 17 00 6c 08 74 08 56 01 33 01 52 06 17 00 |R...l.t.V.3.R...|
00001b90 6c 08 74 09 56 01 33 01 52 07 17 00 6c 08 74 0a |l.t.V.3.R...l.t.|
00001ba0 52 08 74 0b 52 09 74 0c 56 00 74 0d 52 08 23 00 |R.t.R.t.V.t.R.#.|
-00001bb0 29 0a da 15 63 6d 70 5f 74 6f 5f 6b 65 79 2e 3c |)...cmp_to_key.<|
+00001bb0 29 0a 7a 15 63 6d 70 5f 74 6f 5f 6b 65 79 2e 3c |).z.cmp_to_key.<|
00001bc0 6c 6f 63 61 6c 73 3e 2e 4b da 03 6f 62 6a 63 02 |locals>.K..objc.|
00001bd0 00 00 00 00 00 00 00 00 00 00 00 02 00 00 00 13 |................|
00001be0 00 00 08 f3 12 00 00 00 80 00 57 10 6e 00 00 00 |..........W.n...|
00001bf0 00 00 00 00 00 00 52 00 23 00 a9 01 4e a9 01 72 |......R.#...N..r|
-00001c00 5c 00 00 00 29 02 72 27 00 00 00 72 5c 00 00 00 |\...).r'...r\...|
+00001c00 5b 00 00 00 29 02 72 27 00 00 00 72 5b 00 00 00 |[...).r'...r[...|
00001c10 73 02 00 00 00 26 26 72 1b 00 00 00 da 08 5f 5f |s....&&r......__|
00001c20 69 6e 69 74 5f 5f da 1e 63 6d 70 5f 74 6f 5f 6b |init__..cmp_to_k|
00001c30 65 79 2e 3c 6c 6f 63 61 6c 73 3e 2e 4b 2e 5f 5f |ey.<locals>.K.__|
@@ -458,7 +458,7 @@
[snip]
I've attached these two .pyc files in case anyone can read pyc and identify what the difference is.
CPython versions tested on:
3.14
Operating systems tested on:
Linux
Activity
aisk commentedon Nov 5, 2026
Thank you for reporting, but I think this is a duplicate of #129724, which has been fixed on main branch.