DEP: polynomial: Be stricter about integral arguments

This changes the behavior for:
* The `deg`  and `axis` arguments of `<type>der`
* The `deg`  and `axis` arguments of `<type>int`
* The `deg`  argument of `<type>gauss`
* The `deg`  argument of `<type>vander2d`
* The `deg`  argument of `<type>vander3d`

The old behavior was:
* Raise `ValueError` if the argument is a float, but not an integral one
* Allow a float like `1.0` to mean `1`.

This is inconsistent with most other integer-accepting APIs in numpy, which require these to be actual integers, and raise TypeError when they are not.

The new behavior is:
* Raise `TypeError` if the argument is a float, but not an integral one
* Emit a `DeprecationWarning` if a float like `1.0` is passed, continuing to allow it its old meaning.

1 files changed, 9 insertions, 0 deletions

diff --git a/doc/release/1.17.0-notes.rst b/doc/release/1.17.0-notes.rst
index d8ece4244..6440cdd60 100644
--- a/doc/release/1.17.0-notes.rst
+++ b/doc/release/1.17.0-notes.rst
@@ -18,6 +18,15 @@ New functions
 Deprecations
 ============
 
+``np.polynomial`` functions warn when passed ``float``s in place of ``int``s
+----------------------------------------------------------------------------
+Previously functions in this module would accept ``float``s provided their
+values were integral. For consistency with the rest of numpy, doing so is now
+deprecated, and in future will raise a ``TypeError``.
+
+Similarly, passing a float like ``0.5`` in place of an integer will now raise a
+``TypeError`` instead of the previous ``ValueError``.
+
 
 Future Changes
 ==============