issue informative warning when calling legend() without labelled objects.

NNemec · NNemec · commit 17dd254b4441 · 2007-07-13T12:47:31.000Z
svn path=/trunk/matplotlib/; revision=3507
diff --git a/lib/matplotlib/axes.py b/lib/matplotlib/axes.py
@@ -2960,6 +2960,9 @@ def get_handles():
                 if label is not None and label != '' and not label.startswith('_'):
                     handles.append(handle)
                     labels.append(label)
+            if len(handles) == 0:
+                warnings.warn("No labeled objects found. Use label='...' kwarg on individual plots.")
+                return None
 
         elif len(args)==1:
             # LABELS
