DOC: Improve doc wording of data parameter

See matplotlib#9844 (comment)

Author: timhoffm

lib/matplotlib/__init__.py

@@ -1377,10 +1377,10 @@ def _add_data_doc(docstring, replace_names):
 
     data_doc = ("""\
     If given, all parameters also accept a string ``s``, which is
-    interpreted as ``data[s]`` (unless this raises an exception)."""
+    interpreted as ``data[s]`` if ``s`` is a key in ``data``."""
                 if replace_names is None else f"""\
     If given, the following parameters also accept a string ``s``, which is
-    interpreted as ``data[s]`` (unless this raises an exception):
+    interpreted as ``data[s]`` if ``s`` is a key in ``data``:
 
     {', '.join(map('*{}*'.format, replace_names))}""")
     # using string replacement instead of formatting has the advantages

lib/matplotlib/axes/_axes.py

@@ -2744,7 +2744,7 @@ def barh(self, y, width, height=0.8, left=None, *, align="center",
 
         data : indexable object, optional
             If given, all parameters also accept a string ``s``, which is
-            interpreted as ``data[s]`` (unless this raises an exception).
+            interpreted as ``data[s]`` if  ``s`` is a key in ``data``.
 
         **kwargs : `.Rectangle` properties