[Debian-med-packaging] Bug#1057983: brian: runtime dependency on cython legitimate

[Matthias Klose]

On 14.12.23 15:13, Étienne Mollier wrote:
> Hi Matthias,
> 
> Would it be helpful, for the upcoming transition, to demote the
> dependency to cython3 to a recommendation?
> 
> Matthias Klose, on 2023-12-11:
>> Please check that this dependency can be removed. Most likely this
>> dependency is generated by pybuild, because the setup.py requires
>> Cython in it's 'install_requires' attribute.  Please remove that,
>> after checking that it is not a runtime dependency, and also report
>> that issue upstream for upcoming releases.
>>
>> If the runtime dependency is necessary, please just close this bug
>> report.
> 
> I suspected that python3-brian is one of the few cases where the
> cython3 dependency could be legitimate, so I searched within
> upstream examples and found at least one[1] which, when I
> attempt to run is without cython3, will output warnings and
> informational messages, then crash several steps later, issue
> which is fixed when I install cython3 and rerun the script.

if I understand that correctly, then the extension itself doesn't need 
the dependency, but just an example code to build.  So yes, recommends 
would be better, or split out an -examples or -doc package, where you 
add that again as a dependency.

adding cython3 as an autopkg test dependency should also be ok if the 
tests need cython3.

> [1]: https://brian2.readthedocs.io/en/stable/examples/advanced.compare_GSL_to_conventional.html
> 
> Meddling with GSL looks far fetched for this module's usage
> though, and most functions have implemented mechanisms to
> fallback to numpy when cython3 is not available.  cython3 is
> thus not 100% necessary, but it is useful at runtime.  I checked
> against the existing autopkgtest, and lacking cython3 has no
> influence in that particular context so far.  That being said, a
> number of functions benefit from a substancial (as in 170%, but
> GSL will bump that to a whooping 3500% depending on the target
> CPU) performance boost from running with cython3 available.
> (Speaking of GSL, this one depends on make and libgsl-dev, but
> they look missing from the runtime dependencies for now; g++ is
> part of the suggestions though.)
> 
> Have a nice day,  :)