improved plugin modules

@@ -7,6 +7,12 @@ Moreover, when nodes are attached to a net, they inherit the modules
 from this net. When nodes are merged, their sets of modules is added
 from this net. When nodes are merged, their sets of modules is added
 to build the set of modules of the new node.
 to build the set of modules of the new node.
 
 
+The plugin implements a very basic notion of modules, un particular,
+it does not support hierarchy and when a module is attached to a node,
+it is not possible to remove it. So modules are only a way to remember
+where a node comes from and to tag nodes as we aggregate nets, e.g.,
+through compositions (see plugin `ops`).
+
 Internally, modules are stored in a label called `"modules"` (see
 Internally, modules are stored in a label called `"modules"` (see
 plugin `snakes.plugins.labels`).
 plugin `snakes.plugins.labels`).
 
 
@@ -23,11 +29,17 @@ set(['hello'])
 >>> n2.add_place(Place("r"))
 >>> n2.add_place(Place("r"))
 >>> n2.add_place(Place("s", modules="spam"))
 >>> n2.add_place(Place("s", modules="spam"))
 >>> n = n1|n2
 >>> n = n1|n2
->>> list(sorted((p.name, p.modules()) for p in n.place()))
-[('[p|]', set(['hello'])),
- ('[q|]', set(['hello'])),
- ('[|r]', set(['world'])),
- ('[|s]', set(['world', 'spam']))]
+>>> list(sorted((p.name, list(sorted(p.modules()))) for p in n.place()))
+[('[p|]', ['hello']),
+ ('[q|]', ['hello']),
+ ('[|r]', ['world']),
+ ('[|s]', ['spam', 'world'])]
+>>> n.modules("egg")
+>>> list(sorted((p.name, list(sorted(p.modules()))) for p in n.place()))
+[('[p|]', ['egg', 'hello']),
+ ('[q|]', ['egg', 'hello']),
+ ('[|r]', ['egg', 'world']),
+ ('[|s]', ['egg', 'spam', 'world'])]
 """
 """
 
 
 from snakes.plugins import plugin, new_instance
 from snakes.plugins import plugin, new_instance
@@ -65,8 +77,10 @@ def extend (module) :
         def modules (self, modules=None) :
         def modules (self, modules=None) :
             if modules is None :
             if modules is None :
                 return self.label("modules")
                 return self.label("modules")
-            else :
-                self.label(modules=set(iterate(modules)))
+            mod = set(iterate(modules))
+            self.label(modules=mod)
+            for node in self.node() :
+                node.modules(mod | node.modules())
         def add_place (self, place, **options) :
         def add_place (self, place, **options) :
             mod = set(iterate(options.pop("modules", self.modules())))
             mod = set(iterate(options.pop("modules", self.modules())))
             module.PetriNet.add_place(self, place, **options)
             module.PetriNet.add_place(self, place, **options)