Simplify Results() class (#4579)

ultralytics/engine/results.py

@@ -101,19 +101,18 @@ class Results(SimpleClass):
         self.names = names
         self.path = path
         self.save_dir = None
-        self._keys = ('boxes', 'masks', 'probs', 'keypoints')
+        self._keys = 'boxes', 'masks', 'probs', 'keypoints'
 
     def __getitem__(self, idx):
         """Return a Results object for the specified index."""
-        r = self.new()
-        for k in self.keys:
-            setattr(r, k, getattr(self, k)[idx])
-        return r
+        return self._apply('__getitem__', idx)
 
     def __len__(self):
         """Return the number of detections in the Results object."""
-        for k in self.keys:
-            return len(getattr(self, k))
+        for k in self._keys:
+            v = getattr(self, k)
+            if v is not None:
+                return len(v)
 
     def update(self, boxes=None, masks=None, probs=None):
         """Update the boxes, masks, and probs attributes of the Results object."""
@@ -125,43 +124,34 @@ class Results(SimpleClass):
         if probs is not None:
             self.probs = probs
 
+    def _apply(self, fn, *args, **kwargs):
+        r = self.new()
+        for k in self._keys:
+            v = getattr(self, k)
+            if v is not None:
+                setattr(r, k, getattr(v, fn)(*args, **kwargs))
+        return r
+
     def cpu(self):
         """Return a copy of the Results object with all tensors on CPU memory."""
-        r = self.new()
-        for k in self.keys:
-            setattr(r, k, getattr(self, k).cpu())
-        return r
+        return self._apply('cpu')
 
     def numpy(self):
         """Return a copy of the Results object with all tensors as numpy arrays."""
-        r = self.new()
-        for k in self.keys:
-            setattr(r, k, getattr(self, k).numpy())
-        return r
+        return self._apply('numpy')
 
     def cuda(self):
         """Return a copy of the Results object with all tensors on GPU memory."""
-        r = self.new()
-        for k in self.keys:
-            setattr(r, k, getattr(self, k).cuda())
-        return r
+        return self._apply('cuda')
 
     def to(self, *args, **kwargs):
         """Return a copy of the Results object with tensors on the specified device and dtype."""
-        r = self.new()
-        for k in self.keys:
-            setattr(r, k, getattr(self, k).to(*args, **kwargs))
-        return r
+        return self._apply('to', *args, **kwargs)
 
     def new(self):
         """Return a new Results object with the same image, path, and names."""
         return Results(orig_img=self.orig_img, path=self.path, names=self.names)
 
-    @property
-    def keys(self):
-        """Return a list of non-empty attribute names."""
-        return [k for k in self._keys if getattr(self, k) is not None]
-
     def plot(
             self,
             conf=True,