no duplicate warnings, only check for path existence if load accepts file

src/store.py

@@ -35,7 +35,9 @@ class load_or_create:
         plain_text=False
     ):
         self.load=with_filtered_args(load)[0]
+        self.load_arg_names = {p.name for p in inspect.signature(load).parameters.values()}
         self.save=with_filtered_args(save)[0]
+        self.save_arg_names = {p.name for p in inspect.signature(save).parameters.values()}
         self.path_fn=path_fn
         self.hash_len=hash_len
         self.save_args=save_args
@@ -53,35 +55,66 @@ class inner(load_or_create):
 
     def __call__(self, *args, **kwargs):
         # Store the keyword arguments into json and hash it to get the storage path.
-        json_args = self.to_json(**kwargs)
         path = self.path(*args, **kwargs)
-        # path = self.path(hash)
 
-        # If the storage path exists, load the cached object from there.
-        if path.exists():
-            with open(path, "r" if self.plain_text else "rb") as file:
-                # If specified, the first line is a json of the keyword arguments.
-                if self.save_args:
-                    file.readline()
-                return self.load(**self.args_to_kwargs(args, kwargs, path=path, file=file))
+        obj = self.load_wrapper(**self.args_to_kwargs(args, kwargs, path=path))
+        if obj is not None: return obj
 
-        # Else, run the function. and store its result.
         obj = self.fn(*args, **kwargs)
+        if obj is None: return obj
 
-        if obj is None:
-            return obj
-
-        path.parent.mkdir(parents=True, exist_ok=True)
-        with open(path, "w" if self.plain_text else "wb") as file:
-            if self.save_args:
-                file.write(json_args)
-            self.save(obj, **self.args_to_kwargs(args, kwargs, path=path, file=file))
+        self.save_wrapper(obj, **self.args_to_kwargs(args, kwargs, path=path))
 
         return obj
 
     def args_to_kwargs(self, args, kwargs, **extra):
         return extra | kwargs | {self.arg_names[i]: a for i, a in enumerate(args)}
 
+    def load_wrapper(self, **load_args):
+        """
+        load_wrapper returns None or an abject.
+        Iff it returns None, the object is deemed not-loaded and thus,
+        self.fn needs to be called to create the object.
+        It can return None, because self.load returns None or if self.load
+        expects an open file, but no such file exists.
+        """
+        # Check whether self.load does not expect an open file.
+        if "file" in load_args or "file" not in self.load_arg_names:
+            return self.load(**load_args)
+
+        path = load_args["path"]
+        # If self.load expects an open file but there is none, run self.fn.
+        if not path.exists():
+            return None
+
+        with open(path, "r" if self.plain_text else "rb") as file:
+            # If specified, the first line is a json of the keyword arguments.
+            if self.save_args:
+                file.readline()
+            return self.load(**{"file": file} | load_args)
+
+
+    def save_wrapper(self, obj, path, **save_args):
+        """Only open a file if the save function requests you to.
+        """
+        Path(path).parent.mkdir(parents=True, exist_ok=True)
+        if "file" not in self.save_arg_names:
+            return self.save(obj, **{"path": path} | save_args)
+
+        if "file" in save_args:
+            file = save_args["file"]
+        else:
+            file = open(path, "w" if self.plain_text else "wb")
+
+        if self.save_args:
+            file.write(self.to_json(**save_args))
+
+        self.save(obj, **{"file": file, "path": path} | save_args)
+
+        if "file" not in save_args:
+            file.close()
+
+
     def to_json(self, **kwargs) -> bytes:
         """Serialize all keyword arguments to json. 
         We never serialize positional arguments"""

src/warning.py

@@ -14,5 +14,10 @@ class ToDoWarning(Warning):
     def __str__(self):
         return repr(self.message)
 
+PAST_TODO_MESSAGES = set()
+
 def todo(msg):
-    warnings.warn(msg, ToDoWarning)
+    global PAST_TODO_MESSAGES
+    if msg not in PAST_TODO_MESSAGES:
+        warnings.warn(msg, ToDoWarning)
+        PAST_TODO_MESSAGES.add(msg)