ENH: Allow AxisErrors to have a prefix on the message

Moving the string formatting to python makes this a lot easier

1 files changed, 14 insertions, 1 deletions

diff --git a/numpy/core/_internal.py b/numpy/core/_internal.py
index 11a13026b..f25159d8e 100644
--- a/numpy/core/_internal.py
+++ b/numpy/core/_internal.py
@@ -631,4 +631,17 @@ class TooHardError(RuntimeError):
     pass
 
 class AxisError(ValueError, IndexError):
-    pass
+    """ Axis supplied was invalid. """
+    def __init__(self, axis, ndim=None, msg_prefix=None):
+        # single-argument form just delegates to base class
+        if ndim is None and msg_prefix is None:
+            msg = axis
+
+        # do the string formatting here, to save work in the C code
+        else:
+            msg = ("axis {} is out of bounds for array of dimension {}"
+                   .format(axis, ndim))
+            if msg_prefix is not None:
+                msg = "{}: {}".format(msg_prefix, msg)
+
+        super(AxisError, self).__init__(msg)