pytest segfault, not with -v

[Dieter Maurer]

Marco Sulla wrote at 2021-12-18 21:01 +0100:
>Emh, maybe I was not clear. I created a C extension and it segfaults.
>So I created that script to see where it segfaults. But the script
>does not segfault. My doubt is: is that because I'm using eval and
>exec in the script?

The segfault in your C extension is likely caused by a memory management
error. The effects of such errors are typically non local and
apparently non deterministic: small things can decide whether
you see or do not see such an effect.

Use other tools (than a script) to hunt memory management errors.

Python has a compile time option which can help (I forgot its name,
but when you search for Python compile time options, you should
find it): it puts marks before and after the memory areas used for
objects allocated via its API and checks that those marks remain intact.
There is some chance that effects of Memory management errors are
detected earlier by those checks and therefore easier to analyse.

There are specialized tools for the analysis of memory management
errors, e.g. `valgrind/memcheck`. Use one of those for complex problems.


Python's memory management rules (to be observed by C extensions)
are complex. It is quite easy to violate them.

For this reason, I try not to directly write C extensions for Python
but let them generate by `cython`.
The source of a `cython` program resembles Python source code
with extensions. The extensions control the compilation to C,
mostly for optimization purposes. For example, there is a
declaration to mark a variable as a C (rather than Python) variable.
When `cython` compiles the program to "C", it observes
all the complex rules of the Python C API.