[cctbxbb] boost python conversions help needed

Gabor Bunkoczi gabor.bunkoczi at googlemail.com
Wed Sep 30 01:59:02 PDT 2020

Hi Graeme,

I am not sure how useful this is going to be, but here are two strategies
to deal with this scenario:

1. You can query the Python converter registry to see that a converter for
a particular type has been registered, e.g. as it is done here:


This is useful when you want to export something with a particular name,
but share the implementation with something pre-existing (e.g. size_t being

2. You can uniquify the types you are exporting, e.g. as it is done here :


This is useful when you want to export a unique list, but the
uniqueness depends on e.g. the architecture, as for size_t.

Unfortunately, these are only useful when exports are centralised, as
unconditional class_ statements will cause the same warning to be emitted.

BW, Gabor

On Wed, Sep 30, 2020 at 6:30 AM Winter, Graeme (DLSLtd,RAL,LSCI) <
Graeme.Winter at diamond.ac.uk> wrote:

> <bump>
> Does anyone know about this stuff or am I on my own here?
> Alternative of using numpy arrays to do the job has been suggested but
> would prefer keeping in the cctbx ecosystem
> Thanks Graeme
> On 28 Sep 2020, at 07:15, Winter, Graeme (DLSLtd,RAL,LSCI) <
> graeme.winter at diamond.ac.uk> wrote:
> Hi All,
> In the branch
> https://github.com/cctbx/cctbx_project/tree/fixed-width-int-types
> I am working to add a full range of fixed-width integer types to allow
> explicit reading of binary data without conversion from images (amongst
> other things) - mostly I’ve got something _working_ but tests fail because
> stdout / err contains
>   Standard error:
>   /Users/graeme/svn/cctbx/conda_base/python.app/Contents/lib/python3.6/importlib/_bootstrap.py:219: RuntimeWarning:
> to-Python converter for scitbx::af::shared<unsigned int> already
> registered; second conversion method ignored.
> has anyone got any hints where these may be registered?
> The details of the low level flex implementation seems to be minimally
> documented, and the error has no useful stack trace, so I am at a bit of a
> loss as to where the other unsigned int conversion is registered.
> Some pointers from someone who has delved into these in the past would be
> welcome - I have spent a couple days trying to find what I am doing wrong
> and have so far failed - hopefully someone on the list knows their way
> around in here
> Cheers Graeme
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