diff --git a/pytriqs/wrap_generator/wrap_generator.py b/pytriqs/wrap_generator/wrap_generator.py
index 366bd23b..9b20438d 100644
--- a/pytriqs/wrap_generator/wrap_generator.py
+++ b/pytriqs/wrap_generator/wrap_generator.py
@@ -276,7 +276,6 @@ class class_ :
       # Init arithmetic
       # expect a tuple : "algebra", "scalar1", "scalar2", etc...
       self.number_protocol = {}
-      if not isinstance(arithmetic, tuple) : arithmetic = (arithmetic,)
       if arithmetic :
           if not isinstance(arithmetic, tuple) : arithmetic = (arithmetic,)
           add =  arithmetic[0] in ("algebra", "abelian_group", "vector_space", "only_add")
@@ -361,15 +360,25 @@ class class_ :
         #assert 'calling_pattern' not in kw, "No calling_pattern here"
         if  'calling_pattern' not in kw : kw['c_name'] = "__init__"
         f = cfunction(is_constructor = True, **kw)
-        build_type = regular_type_if_view_else_type(self.c_type) if self.c_type_is_view and build_from_regular_type else self.c_type
         all_args = ",".join([ ('*' if t in module_.wrapped_types else '') + n  for t,n,d in f.args])
-        #all_args = ",".join([ ('*' if t in module_.wrapped_types else '') + n + (' = ' + d if d else '') for t,n,d in f.args])
-        if  'calling_pattern' not in kw :
-           f._calling_pattern = "((%s *)self)->_c ->"%self.py_type + ('operator =' if not self.c_type_is_view else 'rebind') + " (%s (%s));"%(build_type,all_args)
-        else : 
-            f._calling_pattern = kw['calling_pattern'] + "\n ((%s *)self)->_c ->"%self.py_type + ('operator =' if not self.c_type_is_view else 'rebind') + " (std::move(result));"
+        ##all_args = ",".join([ ('*' if t in module_.wrapped_types else '') + n + (' = ' + d if d else '') for t,n,d in f.args])
+        # First version, where _new method use the default constructor
+        #build_type = regular_type_if_view_else_type(self.c_type) if self.c_type_is_view and build_from_regular_type else self.c_type
+        #if  'calling_pattern' not in kw :
+        #   f._calling_pattern = "((%s *)self)->_c ->"%self.py_type + ('operator =' if not self.c_type_is_view else 'rebind') + " (%s (%s));"%(build_type,all_args)
+        #else :
+        #    f._calling_pattern = kw['calling_pattern'] + "\n ((%s *)self)->_c ->"%self.py_type + ('operator =' if not self.c_type_is_view else 'rebind') + " (std::move(result));"
+        # Second version : using no default construction, but leaving the
+        # pointer null after _new
+        f._calling_pattern = ''
+        if  'calling_pattern' in kw :
+          f._calling_pattern, all_args = kw['calling_pattern'] + '\n', "std::move(result)"
+        if self.c_type_is_view and build_from_regular_type :
+          f._calling_pattern += "((%s *)self)->_c = new %s(%s (%s));"%(self.py_type, self.c_type,regular_type_if_view_else_type(self.c_type),all_args)
+        else :
+          f._calling_pattern += "((%s *)self)->_c = new %s (%s);"%(self.py_type, self.c_type,all_args)
 
-        if not self.constructor : 
+        if not self.constructor :
             self.constructor = pyfunction(py_name = "__init__", **kw)
             self.constructor.is_constructor = True
         self.constructor.overloads.append(f)
diff --git a/pytriqs/wrap_generator/wrapper.mako.cpp b/pytriqs/wrap_generator/wrapper.mako.cpp
index 600f23a2..66ec68f2 100644
--- a/pytriqs/wrap_generator/wrapper.mako.cpp
+++ b/pytriqs/wrap_generator/wrapper.mako.cpp
@@ -151,11 +151,12 @@ static PyObject* ${c.py_type}_new(PyTypeObject *type, PyObject *args, PyObject *
   self = (${c.py_type} *)type->tp_alloc(type, 0);
   if (self != NULL) {
    try {
-   %if not c.c_type_is_view :
-    self->_c = new ${c.c_type}{};
-   %else :
-    self->_c = new ${c.c_type}{typename ${c.c_type}::regular_type{}}; // no default constructor for views
-   %endif
+   self->_c = NULL;
+   ##//%if not c.c_type_is_view :
+   ##// self->_c = new ${c.c_type}{};
+   ##//%else :
+   ##// self->_c = new ${c.c_type}{typename ${c.c_type}::regular_type{}}; // no default constructor for views
+   ##//%endif
    }
    catch (std::exception const & e) { 
     std::cout  << e.what()<<std::endl;
@@ -168,7 +169,7 @@ static PyObject* ${c.py_type}_new(PyTypeObject *type, PyObject *args, PyObject *
 
 // dealloc
 static void ${c.py_type}_dealloc(${c.py_type}* self) {
-  delete self->_c;
+  if (self->_c != NULL) delete self->_c; // should never be null, but I protect it anyway
   self->ob_type->tp_free((PyObject*)self);
 }
 
@@ -365,7 +366,6 @@ static PyTypeObject ${c.py_type}Type = {
     ${c.py_type}_new,                 /* tp_new */
 };
 
-
 //--------------------- converters for the class c -----------------------------
 
 namespace triqs { namespace py_tools { 
@@ -381,10 +381,18 @@ template <> struct py_converter<${c.c_type}> {
   return (PyObject *)self;
  }
  
- static ${c.c_type} & py2c(PyObject * ob){ return *(((${c.py_type}*)ob)->_c);}
+ static ${c.c_type} & py2c(PyObject * ob){
+  auto *_c = ((${c.py_type} *)ob)->_c;
+  if (_c == NULL) TRIQS_RUNTIME_ERROR << "Severe internal error : _c is null in py2c for type ${c.c_type} !";
+  return *_c;
+ }
  
  static bool is_convertible(PyObject *ob, bool raise_exception){  
-  if (PyObject_TypeCheck(ob, & ${c.py_type}Type)) return true;
+  if (PyObject_TypeCheck(ob, & ${c.py_type}Type)) {
+   if (((${c.py_type} *)ob)->_c != NULL) return true;
+   if (raise_exception) PyErr_SetString(PyExc_TypeError, "Severe internal error : Python object of ${c.py_type} has a _c NULL pointer !!");
+   return false;
+  }
   if (raise_exception) PyErr_SetString(PyExc_TypeError, "Python object is not a ${c.py_type}");
   return false;
  }
diff --git a/triqs/lattice/tight_binding.hpp b/triqs/lattice/tight_binding.hpp
index 6c608755..4fd580fd 100644
--- a/triqs/lattice/tight_binding.hpp
+++ b/triqs/lattice/tight_binding.hpp
@@ -39,8 +39,6 @@ namespace lattice {
   ///
   tight_binding(bravais_lattice const& bl, std::vector<std::vector<long>> all_disp, std::vector<matrix<dcomplex>> all_matrices);
  
-  tight_binding() = default;
-
   /// Underlying lattice
   bravais_lattice const& lattice() const { return bl_; }