More robust handling of exceptions and types

afvincent · afvincent · commit d4bd0cf5d338 · 2017-03-09T21:31:57.000+01:00
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -918,23 +918,33 @@ def _validate_linestyle(ls):
     if isinstance(ls, six.string_types):
         try:
             return _validate_named_linestyle(ls)
-        except KeyError:
-            pass
-
-    # On-off ink (in points) sequence *of even length*.
+        except (UnicodeDecodeError, KeyError):
+            # On Python 2, string-like *ls*, like for example
+            # 'solid'.encode('utf-16'), may raise a unicode error.
+            raise ValueError("the linestyle string is not a valid string.")
+
+    if hasattr(ls, 'decode'):
+        # On Python 2, a string-like *ls* should already have lead to a
+        # successful return or to raising an exception. On Python 3, we have
+        # to manually raise an exception in the case of a byte-like *ls*.
+        # Otherwise, if *ls* is of even-length, it will be passed to the
+        # instance of validate_nseq_float, which will return an absurd on-off
+        # ink sequence...
+        raise ValueError("linestyle neither looks like an on-off ink sequence "
+                         "nor a valid string.")
+
+    # Look for an on-off ink sequence (in points) *of even length*.
     # Offset is set to None.
     try:
         if len(ls) % 2 != 0:
-            # Expecting a sequence of even length
-            raise ValueError
+            raise ValueError("the linestyle sequence is not of even length.")
+
         return (None, validate_nseq_float()(ls))
-    except (ValueError, TypeError):
-        # TypeError can be raised by wrong types passed to float()
-        # (called inside the instance of validate_nseq_float).
-        pass
 
-    raise ValueError("linestyle must be a valid string or "
-                     "an even-length sequence of floats.")
+    except (ValueError, TypeError):
+        # TypeError can be raised inside the instance of validate_nseq_float,
+        # by wrong types passed to float(), like NoneType.
+        raise ValueError("linestyle is not a valid on-off ink sequence.")
 
 
 # a map from key -> value, converter
