While working on reproducible builds for openSUSE, I found that
our python-numpy package varied in every build

at least the 311, 310 and 39 versions of
/usr/lib64/python3.9/site-packages/numpy-1.25.2.dist-info/RECORD vary thus:
-numpy/core/_multiarray_umath.cpython-39-x86_64-linux-gnu.so,sha256=AqheHmg2MFytBdKCCIY2DO8dHS58gSmAuy3hkJclqmo,40188336^M
+numpy/core/_multiarray_umath.cpython-39-x86_64-linux-gnu.so,sha256=nlzKMAtipwUy5z6eV6KpruSJC2Mx8mfPz_dTyosfhPM,40188336^M

even when the final .so files came out identical.
The reason is that the .so gets compiled twice:
once by setup.py build
and then again by setup.py install
This makes debugging rather hard.


at one point, I captured this 4-byte-diff:
> filterdiff hexdump\ -C ./RPMS*/usr/lib64/python3.9/site-packages/numpy/core/_multiarray_umath.cpython-39-x86_64-linux-gnu.so
--- hexdump -C ./RPMS.1/usr/lib64/python3.9/site-packages/numpy/core/_multiarray_umath.cpython-39-x86_64-linux-gnu.so
+++ hexdump -C ./RPMS.2/usr/lib64/python3.9/site-packages/numpy/core/_multiarray_umath.cpython-39-x86_64-linux-gnu.so
@@ -403654,7 +403654,7 @@
 0066e610  5f 6d 75 6c 74 69 61 72  72 61 79 5f 75 6d 61 74  |_multiarray_umat|
 0066e620  68 2e 63 70 79 74 68 6f  6e 2d 33 39 2d 78 38 36  |h.cpython-39-x86|
 0066e630  5f 36 34 2d 6c 69 6e 75  78 2d 67 6e 75 2e 73 6f  |_64-linux-gnu.so|
-0066e640  2e 64 65 62 75 67 00 00  84 ef 54 21 00 2e 73 68  |.debug....T!..sh|
+0066e640  2e 64 65 62 75 67 00 00  79 21 36 45 00 2e 73 68  |.debug..y!6E..sh|
 0066e650  73 74 72 74 61 62 00 2e  6e 6f 74 65 2e 67 6e 75  |strtab..note.gnu|
 0066e660  2e 70 72 6f 70 65 72 74  79 00 2e 6e 6f 74 65 2e  |.property..note.|
 0066e670  67 6e 75 2e 62 75 69 6c  64 2d 69 64 00 2e 67 6e  |gnu.build-id..gn|

which has something to do with debug symbols.