[Numpy-discussion] function name as parameter

[Zachary Pincus]

> Hi Robert,
> so in a big data analysis framework, that is essentially written in C 
> ++,
> exposed to python with SWIG, plus dedicated python modules, the user
> performs an analysis choosing some given modules by name,as in :
> myOpt="foo"
> my_analyse.perform(use_optimizer=myOpt)
>
> The attribute use_optimizer is then checked to perform the right
> calls/instantiations of python but also C++ objects..... and the  
> actual
> crunching number is in the C++ part.
> But then I realize that I need to tweak this optimizer's state, and  
> the
> optimizer object is accessible from a library pyOpt that has been
> swigified from a C++ library.
> Then I access the object by calling optObject =
> eval("pyOpt.%s(some_args)"%myOpt)
> where myOpt would be "foo" in this particular analysis. This is  
> because
> what the attribute use_optimizer expects is also the object name in  
> the
> library, of course.
> It goes without saying that I could do :
> if myOpt=="foo":
>     optObject=pyOpt.foo(some_args)
> else:
>     ....
> and if you guys tell me it is way safer, I will do that instead of the
> use of eval that I liked because of the compactness.....

Well, optObject=getattr(pyOpt, myOpt) is a bit nicer and marginally  
more likely to return sane error messages than optObject=eval("pyOpt. 
%s"%myOpt). Then you could do result=optObject(some_args)...

But why not have the user just pass in the relevant optObject from the  
pyOpt namespace (or some restricted namespace that just has the  
relevant functions exposed)? E.g.
my_analysis.perform(optimizer=pyOpt.Amoeba)
rather than
my_analysis.perform(optimizer='Amoeba')

This lets users do introspection on the pyOpt namespace to see what  
functions they can choose from, which is rather friendlier in an  
interactive environment.

Zach