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, 8 insertions, 18 deletions

diff --git a/numpy/polynomial/chebyshev.py b/numpy/polynomial/chebyshev.py
index 5f69bf338..475582fdc 100644
--- a/numpy/polynomial/chebyshev.py
+++ b/numpy/polynomial/chebyshev.py
@@ -910,14 +910,10 @@ def chebder(c, m=1, scl=1, axis=0):
     c = np.array(c, ndmin=1, copy=1)
     if c.dtype.char in '?bBhHiIlLqQpP':
         c = c.astype(np.double)
-    cnt, iaxis = [int(t) for t in [m, axis]]
-
-    if cnt != m:
-        raise ValueError("The order of derivation must be integer")
+    cnt = pu._deprecate_as_int(m, "the order of derivation")
+    iaxis = pu._deprecate_as_int(axis, "the axis")
     if cnt < 0:
         raise ValueError("The order of derivation must be non-negative")
-    if iaxis != axis:
-        raise ValueError("The axis must be integer")
     iaxis = normalize_axis_index(iaxis, c.ndim)
 
     if cnt == 0:
@@ -1033,10 +1029,8 @@ def chebint(c, m=1, k=[], lbnd=0, scl=1, axis=0):
         c = c.astype(np.double)
     if not np.iterable(k):
         k = [k]
-    cnt, iaxis = [int(t) for t in [m, axis]]
-
-    if cnt != m:
-        raise ValueError("The order of integration must be integer")
+    cnt = pu._deprecate_as_int(m, "the order of integration")
+    iaxis = pu._deprecate_as_int(axis, "the axis")
     if cnt < 0:
         raise ValueError("The order of integration must be non-negative")
     if len(k) > cnt:
@@ -1045,8 +1039,6 @@ def chebint(c, m=1, k=[], lbnd=0, scl=1, axis=0):
         raise ValueError("lbnd must be a scalar.")
     if np.ndim(scl) != 0:
         raise ValueError("scl must be a scalar.")
-    if iaxis != axis:
-        raise ValueError("The axis must be integer")
     iaxis = normalize_axis_index(iaxis, c.ndim)
 
     if cnt == 0:
@@ -1406,9 +1398,7 @@ def chebvander(x, deg):
         the converted `x`.
 
     """
-    ideg = int(deg)
-    if ideg != deg:
-        raise ValueError("deg must be integer")
+    ideg = pu._deprecate_as_int(deg, "deg")
     if ideg < 0:
         raise ValueError("deg must be non-negative")
 
@@ -1858,9 +1848,9 @@ def chebgauss(deg):
     .. math:: w_i = \\pi / n
 
     """
-    ideg = int(deg)
-    if ideg != deg or ideg < 1:
-        raise ValueError("deg must be a non-negative integer")
+    ideg = pu._deprecate_as_int(deg, "deg")
+    if ideg <= 0:
+        raise ValueError("deg must be a positive integer")
 
     x = np.cos(np.pi * np.arange(1, 2*ideg, 2) / (2.0*ideg))
     w = np.ones(ideg)*(np.pi/ideg)