[C++-sig] functools.partial vs boost::python

[troy d. straszheim]

Neal Becker wrote:
> Has anyone noticed that a function created with boost::python using
> args() to give keyword arguments doesn't seem to work with 
> functools.partial keyword arguments (but does with positional args)?
> 
> For example, I have this function:
>   class_<boost_uniform_real_wrap>
>     ("uniform_real", "Uniform float distribution", 
> bp::init<rng_t&,double,double>(
> 	(bp::arg ("rng"),
> 	 bp::arg ("min"),
> 	 bp::arg ("max"))...
> 
> Then:
> from functools import partial
> f = partial (uniform_real, rng=rng1) << using keyword doesn't work
> f (1,2)
> ArgumentError: Python argument types in
>     uniform_real.__init__(uniform_real, int, int)
> did not match C++ signature:
>     __init__(_object*, boost::random::mersenne_twister<unsigned int, 
> 32, 624, 397, 31, 2567483615u, 11, 7, 2636928640u, 15, 4022730752u, 
> 18, 3346425566u> {lvalue} rng, double min, double max)
> 
> But this works:
> from functools import partial
> f = partial (uniform_real, rng1) << pos arg does work
> 
> In [27]: f(1,2)
> Out[27]: uniform_real(1,2)
> 

That doesn't work for pure python functions either:

 >>> def f(x,y,z): return x*100 + y*10 + z
...
 >>> from functools import partial as p
 >>> p(f,x=1)(2,3)
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
TypeError: f() got multiple values for keyword argument 'x'
 >>> p(f,x=1)(y=2,z=3)
123
 >>> p(f,1)(2,3)
123

The error message is misleading for sure.  Boost.python is going through 
a list of overloads and trying them in order; if it runs out of 
overloads, it says nothing matched.  I think I can get it to be smarter 
about this, lemme see...

-t