Bug#1117208: python3-numpy: Can't find libblas and liblapack

[Simon McVittie]

Control: reassign -1 libblas3 3.12.1-6
Control: affects -1 + python3-numpy
Control: tags -1 + moreinfo

On Sat, 04 Oct 2025 at 22:00:13 +0200, Matthias Urlichs wrote:
>I had to do this:
>
>/usr/lib/x86_64-linux-gnu$ sudo ln -s blas/libblas.so.3 .
>/usr/lib/x86_64-linux-gnu$ sudo ln -s lapack/liblapack.so.3 .
>
>... to get a plain "import numpy" to work.

This sounds like a problem with the libblas.so.3 alternative. The way it 
is meant to work is something like this:

/usr/lib/x86_64-linux-gnu/libblas.so.3
-> /etc/alternatives/libblas.so.3-x86_64-linux-gnu
-> /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3

and similarly

/usr/lib/x86_64-linux-gnu/liblapack.so.3
-> /etc/alternatives/liblapack.so.3-x86_64-linux-gnu
-> /usr/lib/x86_64-linux-gnu/openblas-pthread/liblapack.so.3

(but you might have a different implementation of the alternatives, like 
the reference implementations libblas3 and liblapack3, which are in blas 
and lapack directories instead of the openblas-pthread directory that 
contains the implementation used on my system).

If I understand the overall system correctly, numpy is meant to load the 
basenames libblas.so.3 and liblapack.so.3, which in practice means 
/usr/lib/x86_64-linux-gnu/libblas.so.3 and 
/usr/lib/x86_64-linux-gnu/liblapack.so.3, and the various 
implementations of the libblas.so.3 and liblapack.so.3 virtual packages 
are responsible for providing those; in which case this wouldn't be a 
python3-numpy bug.

Please check /var/log/apt - has something gone wrong with those 
packages' maintainer scripts on your system?

I couldn't immediately reproduce a similar bug by installing 
python3-numpy, libblas3 and liblapack3 into a debian:sid-slim podman 
container.

     smcv