[cctbxbb] controlling types over the C++/Python interface

[David Waterman]

Hi Ralf,

Thanks for the explanation. it's good to know what I shouldn't try to solve
a problem, as I now feel more freely able to get on with solving it :) In
this case the extra overhead of creating scitbx.matrix entities from the
returned tuples will disappear with time, as more code gets moved to C++.
So I must keep in mind not to worry about performance at the Python level.

I have a better feel for the type mappings now I think. Tuple as a common
type for all sequence-type objects makes sense in Python, and as long as I
can expect to get tuples back I can avoid any nasty surprises.

-- David


On 14 May 2012 15:15, Ralf Grosse-Kunstleve <rwgrosse-kunstleve at lbl.gov>wrote:

> Hi David,
>
> When I access the attribute in Python with the usual dot operator I get a
>> tuple. What I'd really like though is an object of type <class
>> 'scitbx.matrix.col'>, which is what I passed to the constructor of the
>> object in Python.
>>
>
> This would be nice indeed but is a little tricky to implement. The C++
> wrapper code would need to import scitbx.matrix. It's entirely possible but
> I always shied away from introducing this dependency.
>
>
>> I found I had to add
>>
>> from cctbx.array_family import flex
>>
>> to the package __init__.py where my C++ extension is imported,
>>
>
> This import piggy-backs a whole bunch of loosely related from-and-to-tuple
> conversions; see scitbx/array_family/boost_python/flex_ext.cpp. I had long
> discussions with Luc about this when he started using cctbx, because from a
> purists standpoint centralizing all the conversions in flex_ext.cpp breaks
> modularity. However, the discussions didn't lead to practical alternatives,
> and I believe the current solution works well in practice.
>
> Ralf
>
>
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