add user_dict for caching (#4501)

* add user_dict for caching

* add description in docs

* doc syntax fix

* what line?

docs/nodes/script/script1_lite.rst

@@ -29,6 +29,15 @@ Features
 - You must declare an input socket, but outputs are optional.
 - You can set defaults for input numbers, vectors, and list sockets.
 - You can set the level of nestedness; means you don't need to unwrap/index stuff via code
+- You can use a dictionary per node instance, this allows you to store any data that can be produced at runtime. Get a `dict` and store states using these functions ::
+
+    # here self refers to the node and will be available at runtime.
+    dict = self.get_user_dict()
+    self.reset_user_dict()   # takes a boolean parameter "hard" to wipe the 
+    ...                      # dictionaries at the class-level (all instances)
+    ...                      # hard=True is useful for debugging.
+
+
 - You can append a UI drawing function to the default drawing function of SNLite, in case you want to display a variety of UI elements from anywhere in Blender in one place.
 - has the option to **auto inject** the list of variable references as **parameters** much like javascript does for **arguments** inside a function. In essence implemented like this ::
 

nodes/script/script1_lite.py

@@ -161,9 +161,24 @@ def make_operator(self, new_func_name, force=False):
     script_name: StringProperty()
     script_str: StringProperty()
     node_dict = {}
+    user_dict = {}
 
     halt_updates: BoolProperty(name="snlite halting token")
 
+    def get_user_dict(self):
+        if not self.user_dict.get(hash(self)):
+            self.user_dict[hash(self)] = {}
+        return self.user_dict[hash(self)]
+
+    def reset_user_dict(self, hard=False):
+        if hard:
+            # will reset all user_dicts in all instances of snlite.
+            # you probably don't want to do this, but for debugging it can be useful.
+            self.user_dict = {}
+
+        self.user_dict[hash(self)] = {}
+
+
     def updateNode2(self, context):
         if not self.halt_updates:
             updateNode(self, context)
@@ -288,9 +303,6 @@ def update_sockets(self):
 
         return True
 
-
-
-
     def sv_init(self, context):
         self.use_custom_color = False