numpy · charris · Oct 20, 2016 · May 1, 2016 · Oct 8, 2016
diff --git a/doc/release/1.12.0-notes.rst b/doc/release/1.12.0-notes.rst
@@ -73,18 +73,24 @@ DeprecationWarning to error
 * Non-integers used as index values raise ``TypeError``,
   e.g., in ``reshape``, ``take``, and specifying reduce axis.
 
+``power`` and ``**`` raise errors for integer to negative integer powers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The previous behavior was
+
+* zero to negative integer powers returned least integral value.
+* 1, -1 to negative integer powers returned correct values
+* all remaining integers returned zero when raised to negative integer powers.
+
+All of these cases now raise a ``ValueError``. It was felt that a simple rule
+was the best way to go rather than have special exceptions for the units. If
+you need negative powers, use an inexact type.
+
 Relaxed stride checking is the default
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
 This will have some impact on code that assumed that ``F_CONTIGUOUS`` and
 ``C_CONTIGUOUS`` were mutually exclusive and could be set to determine the
 default order for arrays that are now both.
 
-``MaskedArray`` takes view of data **and** mask when slicing
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-XXX
-
-
 ``np.percentile`` 'midpoint' interpolation method fixed for exact indices
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 'midpoint' interpolator now gives the same result as 'lower' and 'higher' when
@@ -93,7 +99,6 @@ the two coincide. Previous behavior of 'lower' + 0.5 is fixed.
 
 ``keepdims`` kwarg is passed through to user-class methods
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
 numpy functions that take a ``keepdims`` kwarg now pass the value
 through to the corresponding methods on ndarray sub-classes.  Previously the
 ``keepdims`` keyword would be silently dropped.  These functions now have

diff --git a/numpy/core/src/umath/loops.c.src b/numpy/core/src/umath/loops.c.src
@@ -787,6 +787,7 @@ BOOL__ones_like(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UN
  *         npy_long, npy_ulong, npy_longlong, npy_ulonglong#
  * #ftype = npy_float, npy_float, npy_float, npy_float, npy_double, npy_double,
  *          npy_double, npy_double, npy_double, npy_double#
+ * #SIGNED = 1, 0, 1, 0, 1, 0, 1, 0, 1, 0#
  */
 
 #define @TYPE@_floor_divide @TYPE@_divide
@@ -959,16 +960,22 @@ NPY_NO_EXPORT void
         @type@ in2 = *(@type@ *)ip2;
         @type@ out;
 
-        if (in2 == 0) {
-          *((@type@ *)op1) = 1;
-          continue;
+#if @SIGNED@
+        if (in2 < 0) {
+            NPY_ALLOW_C_API_DEF
+            NPY_ALLOW_C_API;
+            PyErr_SetString(PyExc_ValueError,
+                    "Integers to negative integer powers are not allowed.");
+            NPY_DISABLE_C_API;
+            return;
         }
-        if (in1 == 1) {
+#endif
+        if (in2 == 0) {
             *((@type@ *)op1) = 1;
             continue;
         }
-        if (in2 < 0 || in1 == 0) {
-            *((@type@ *)op1) = 0;
+        if (in1 == 1) {
+            *((@type@ *)op1) = 1;
             continue;
         }
 

diff --git a/numpy/core/tests/test_regression.py b/numpy/core/tests/test_regression.py
@@ -1242,19 +1242,6 @@ def test_array_ndmin_overflow(self):
         "Ticket #947."
         self.assertRaises(ValueError, lambda: np.array([1], ndmin=33))
 
-    def test_errobj_reference_leak(self, level=rlevel):
-        # Ticket #955
-        with np.errstate(all="ignore"):
-            z = int(0)
-            p = np.int32(-1)
-
-            gc.collect()
-            n_before = len(gc.get_objects())
-            z**p  # this shouldn't leak a reference to errobj
-            gc.collect()
-            n_after = len(gc.get_objects())
-            assert_(n_before >= n_after, (n_before, n_after))
-
     def test_void_scalar_with_titles(self, level=rlevel):
         # No ticket
         data = [('john', 4), ('mary', 5)]

diff --git a/numpy/core/tests/test_umath.py b/numpy/core/tests/test_umath.py
@@ -426,16 +426,43 @@ def test_fast_power(self):
 
     def test_integer_power(self):
         a = np.array([15, 15], 'i8')
-        b = a ** a
+        b = np.power(a, a)
         assert_equal(b, [437893890380859375, 437893890380859375])
 
-    def test_integer_power_with_zero_exponent(self):
-        arr = np.arange(-10, 10)
-        assert_equal(np.power(arr, 0), np.ones_like(arr))
+    def test_integer_power_with_integer_zero_exponent(self):
+        dtypes = np.typecodes['Integer']
+        for dt in dtypes:
+            arr = np.arange(-10, 10, dtype=dt)
+            assert_equal(np.power(arr, 0), np.ones_like(arr))
+
+        dtypes = np.typecodes['UnsignedInteger']
+        for dt in dtypes:
+            arr = np.arange(10, dtype=dt)
+            assert_equal(np.power(arr, 0), np.ones_like(arr))
 
     def test_integer_power_of_1(self):
-        arr = np.arange(-10, 10)
-        assert_equal(np.power(1, arr), np.ones_like(arr))
+        dtypes = np.typecodes['AllInteger']
+        for dt in dtypes:
+            arr = np.arange(10, dtype=dt)
+            assert_equal(np.power(1, arr), np.ones_like(arr))
+
+    def test_integer_power_of_zero(self):
+        dtypes = np.typecodes['AllInteger']
+        for dt in dtypes:
+            arr = np.arange(1, 10, dtype=dt)
+            assert_equal(np.power(0, arr), np.zeros_like(arr))
+
+    def test_integer_to_negative_power(self):
+        dtypes = np.typecodes['Integer']
+        for dt in dtypes:
+            a = np.array([0, 1, 2, 3], dtype=dt)
+            b = np.array([0, 1, 2, -3], dtype=dt)
+            one = np.array(1, dtype=dt)
+            minusone = np.array(-1, dtype=dt)
+            assert_raises(ValueError, np.power, a, b)
+            assert_raises(ValueError, np.power, a, minusone)
+            assert_raises(ValueError, np.power, one, b)
+            assert_raises(ValueError, np.power, one, minusone)
 
 
 class TestLog2(TestCase):