[c++2py] TRIQS/unstable - NB5 ''max() arg is an empty sequence''

[Wentzell]

Using TRIQS/unstable, the following triqs magic copied out of 5-Parameters.ipynb

%%triqs --only g
#include <vector>
#include <string>

struct params{ 
 int i;
 double x=0;   
 double z=3;
 std::string s = "what ?";   
 std::vector<int> v;
};

/// g
CPP2PY_ARG_AS_DICT
double g(params const & a) {
  std::cout << "s = " << a.s << std::endl;  
  return a.i + a.x + a.v.at(0);   
}

fails with

----------------------------c++2py error ----------------------------
Welcome to the wrapper desc file generator of TRIQS, based on libclang !
Parsing the C++ file (may take a few seconds) ...
... done. 
Extracting ...
Analysing params
... done
Parsing C++ code. Generating the wrapper and converters ...
Transforming no argument accessors into Python properties
Generating the converters for parameters classes : params
Traceback (most recent call last):
  File "/home/nwentzel/opt/triqs/bin/c++2py.py", line 159, in <module>
    rendered = tpl.render(classes = classes_of_parameters, args = args, shell_command= shell_command )
  File "/usr/lib/python2.7/site-packages/mako/template.py", line 462, in render
    return runtime._render(self, self.callable_, args, data)
  File "/usr/lib/python2.7/site-packages/mako/runtime.py", line 838, in _render
    **_kwargs_for_callable(callable_, data))
  File "/usr/lib/python2.7/site-packages/mako/runtime.py", line 873, in _render_context
    _exec_template(inherit, lclcontext, args=args, kwargs=kwargs)
  File "/usr/lib/python2.7/site-packages/mako/runtime.py", line 899, in _exec_template
    callable_(context, *args, **kwargs)
  File "_home_nwentzel_opt_triqs_share_triqs_cpp2py_mako_parameters_rst", line 59, in render_body
  File "_home_nwentzel_opt_triqs_share_triqs_cpp2py_mako_parameters_rst", line 43, in doc_format
ValueError: max() arg is an empty sequence

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-3-bc9d327f0455> in <module>()
----> 1 get_ipython().run_cell_magic(u'triqs', u'--only g', u'#include <vector>\n#include <string>\n\nstruct params{ \n int i;\n double x=0;   \n double z=3;\n std::string s = "what ?";   \n std::vector<int> v;\n};\n\n/// g\nCPP2PY_ARG_AS_DICT\ndouble g(params const & a) {\n  std::cout << "s = " << a.s << std::endl;  \n  return a.i + a.x + a.v.at(0);   \n}')

/usr/lib/python2.7/site-packages/IPython/core/interactiveshell.pyc in run_cell_magic(self, magic_name, line, cell)
   2113             magic_arg_s = self.var_expand(line, stack_depth)
   2114             with self.builtin_trap:
-> 2115                 result = fn(magic_arg_s, cell)
   2116             return result
   2117 

<decorator-gen-122> in triqs(self, line, cell)

/usr/lib/python2.7/site-packages/IPython/core/magic.pyc in <lambda>(f, *a, **k)
    186     # but it's overkill for just that one bit of state.
    187     def magic_deco(arg):
--> 188         call = lambda f, *a, **k: f(*a, **k)
    189 
    190         if callable(arg):

/home/nwentzel/opt/triqs/lib/python2.7/site-packages/pytriqs/magic.pyc in triqs(self, line, cell)
    144             only_list = ','.join(args.only)
    145             only_list = (" --only " + only_list) if only_list else ''
--> 146             execute(cpp2py_bin + " ./ext.cpp -p -m ext -o ext" + only_list, "c++2py")
    147 
    148             # Call the wrapper generator

/home/nwentzel/opt/triqs/lib/python2.7/site-packages/pytriqs/magic.pyc in execute(command, message)
    137                 except subprocess.CalledProcessError as E :
    138                    print_out ( message + " error ", E.output)
--> 139                    raise RuntimeError, "Error"
    140                 if args.verbosity>0:
    141                    print_out(message, out)

RuntimeError: Error