ENH: _NoValue class at top-level to test kwargs

Add _NoValue class at top level to make it possible to detect when
non-default values got passed to a keyword argument, as in:

    def func(a, b=np._NoValue):
        if b is not np._NoValue:
            warnings.warn("Argument b is deprecated",
                          DeprecationWarning)

1 files changed, 10 insertions, 0 deletions

diff --git a/numpy/__init__.py b/numpy/__init__.py
index 772c75b63..39933e8ca 100644
--- a/numpy/__init__.py
+++ b/numpy/__init__.py
@@ -132,6 +132,16 @@ class VisibleDeprecationWarning(UserWarning):
     pass
 
 
+class _NoValue:
+    """Special keyword value.
+
+    This class may be used as the default value assigned to a
+    deprecated keyword in order to check if it has been given a user
+    defined value.
+    """
+    pass
+
+
 # oldnumeric and numarray were removed in 1.9. In case some packages import
 # but do not use them, we define them here for backward compatibility.
 oldnumeric = 'removed'