python: second attempt at fixing propagate labels

* resolve the input to a name for the helper
 (this fixes registry issues)
* return if the propagate labels was implemented
 (and call the base implementation if not)

Author: guruofquality

Pothos/Block.py

@@ -51,7 +51,7 @@ def deactivate(self): pass
 
     def work(self): pass
 
-    def propagateLabels(self, input): pass
+    def propagateLabels(self, input): return NotImplemented
 
-    def _propagateLabels(self, input):
-        self.propagateLabels(InputPort(input))
+    def _propagateLabels(self, name):
+        return self.propagateLabels(self.input(name)) is NotImplemented

PythonBlock.cpp

@@ -40,8 +40,11 @@ class PythonBlock : Pothos::Block
 
     void propagateLabels(const Pothos::InputPort *input)
     {
-        //forward to wrapper that casts input object
-        _block.call("_propagateLabels", input);
+        //forward to wrapper that takes input port name
+        auto not_implemeneted = _block.call<bool>("_propagateLabels", input->name());
+
+        //if the overload was not implemented, call base function
+        if (not_implemeneted) Pothos::Block::propagateLabels(input);
     }
 
     Pothos::Object opaqueCallHandler(const std::string &name, const Pothos::Object *inputArgs, const size_t numArgs)