python3 problem with munuit2.cpp

[GoogleCodeExporter]

Tried to follow the instructions on http://code.google.com/p/pyminuit/ using 
Python3 (!!).

This worked. 

However, when I tried to replace in function "f(x,y)" the variable name "x" by 
"xx", I got the error:

  m.migrad()
KeyError:  'Parameter "x" is missing from values'.

I worked out the problem:
in  minuit_Minuit_init() self->upar is set like this:

self->upar->Add(Pystring_AsString(param)),
where "Pystring_AsString(x)" is replaced by "PyUnicode_AS_DATA(x)".

This however only returns a pointer to the first character of "param"

The problem is resolved by replacing the above with

PyObject * ascii_param=PyUnicode_AsASCIIString(param);
self->upar->Add(PyBytes_AsString(ascii_param),value,error);
Py_DECREF(ascii_param);

Original issue reported on code.google.com by [email protected] on 3 Jun 2013 at 9:19