ENH: add np.positive ufunc and use it for ndarray.__pos__

xref GH8932

11 files changed, 113 insertions, 2 deletions

diff --git a/doc/release/1.13.0-notes.rst b/doc/release/1.13.0-notes.rst
index df6ce7c4b..f594c1825 100644
--- a/doc/release/1.13.0-notes.rst
+++ b/doc/release/1.13.0-notes.rst
@@ -327,6 +327,11 @@ regarding "workspace" sizes, and in some places may use faster algorithms.
 This now works on empty arrays, returning 0, and can reduce over multiple axes.
 Previously, a ``ValueError`` was thrown in these cases.
 
+New ``positive`` ufunc
+----------------------
+This ufunc corresponds to unary `+`, but unlike `+` on an ndarray it will raise
+an error if array values do not support numeric operations.
+
 Changes
 =======
 
diff --git a/doc/source/reference/c-api.array.rst b/doc/source/reference/c-api.array.rst
index b50f86e46..35df42daa 100644
--- a/doc/source/reference/c-api.array.rst
+++ b/doc/source/reference/c-api.array.rst
@@ -3129,8 +3129,8 @@ Internal Flexibility
 
         **add**, **subtract**, **multiply**, **divide**,
         **remainder**, **power**, **square**, **reciprocal**,
-        **ones_like**, **sqrt**, **negative**, **absolute**,
-        **invert**, **left_shift**, **right_shift**,
+        **ones_like**, **sqrt**, **negative**, **positive**,
+        **absolute**, **invert**, **left_shift**, **right_shift**,
         **bitwise_and**, **bitwise_xor**, **bitwise_or**,
         **less**, **less_equal**, **equal**, **not_equal**,
         **greater**, **greater_equal**, **floor_divide**,
diff --git a/doc/source/reference/ufuncs.rst b/doc/source/reference/ufuncs.rst
index bcd3d5f0a..94663a141 100644
--- a/doc/source/reference/ufuncs.rst
+++ b/doc/source/reference/ufuncs.rst
@@ -505,6 +505,7 @@ Math operations
     true_divide
     floor_divide
     negative
+    positive
     power
     remainder
     mod
diff --git a/numpy/core/code_generators/generate_umath.py b/numpy/core/code_generators/generate_umath.py
index 4a8566d9d..dfba04c18 100644
--- a/numpy/core/code_generators/generate_umath.py
+++ b/numpy/core/code_generators/generate_umath.py
@@ -398,6 +398,14 @@ defdict = {
           TD(cmplx, f='neg'),
           TD(O, f='PyNumber_Negative'),
           ),
+'positive':
+    Ufunc(1, 1, None,
+          docstrings.get('numpy.core.umath.positive'),
+          'PyUFunc_SimpleUnaryOperationTypeResolver',
+          TD(ints+flts+timedeltaonly),
+          TD(cmplx, f='pos'),
+          TD(O, f='PyNumber_Positive'),
+          ),
 'sign':
     Ufunc(1, 1, None,
           docstrings.get('numpy.core.umath.sign'),
diff --git a/numpy/core/code_generators/ufunc_docstrings.py b/numpy/core/code_generators/ufunc_docstrings.py
index ad4a10d3b..ed9e05b15 100644
--- a/numpy/core/code_generators/ufunc_docstrings.py
+++ b/numpy/core/code_generators/ufunc_docstrings.py
@@ -2537,6 +2537,27 @@ add_newdoc('numpy.core.umath', 'negative',
 
     """)
 
+add_newdoc('numpy.core.umath', 'positive',
+    """
+    Numerical positive, element-wise.
+
+    Parameters
+    ----------
+    x : array_like or scalar
+        Input array.
+
+    Returns
+    -------
+    y : ndarray or scalar
+        Returned array or scalar: `y = +x`.
+
+    Notes
+    -----
+    Equivalent to `x.copy()`, but only defined for types that support
+    arithmetic.
+
+    """)
+
 add_newdoc('numpy.core.umath', 'not_equal',
     """
     Return (x1 != x2) element-wise.
diff --git a/numpy/core/src/umath/funcs.inc.src b/numpy/core/src/umath/funcs.inc.src
index 9887120f5..5613c30ee 100644
--- a/numpy/core/src/umath/funcs.inc.src
+++ b/numpy/core/src/umath/funcs.inc.src
@@ -188,6 +188,14 @@ nc_neg@c@(@ctype@ *a, @ctype@ *r)
 }
 
 static void
+nc_pos@c@(@ctype@ *a, @ctype@ *r)
+{
+    r->real = +a->real;
+    r->imag = +a->imag;
+    return;
+}
+
+static void
 nc_sqrt@c@(@ctype@ *x, @ctype@ *r)
 {
     *r = npy_csqrt@c@(*x);
diff --git a/numpy/core/src/umath/loops.c.src b/numpy/core/src/umath/loops.c.src
index 24364afbd..47faaf180 100644
--- a/numpy/core/src/umath/loops.c.src
+++ b/numpy/core/src/umath/loops.c.src
@@ -833,6 +833,12 @@ NPY_NO_EXPORT void
     }
 }
 
+NPY_NO_EXPORT void
+@TYPE@_positive(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func))
+{
+    UNARY_LOOP_FAST(@type@, @type@, *out = +in);
+}
+
 /**begin repeat1
  * #isa = , _avx2#
  * #ISA = , AVX2#
@@ -1185,6 +1191,15 @@ TIMEDELTA_negative(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY
 }
 
 NPY_NO_EXPORT void
+TIMEDELTA_positive(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func))
+{
+    UNARY_LOOP {
+        const npy_timedelta in1 = *(npy_timedelta *)ip1;
+        *((npy_timedelta *)op1) = +in1;
+    }
+}
+
+NPY_NO_EXPORT void
 TIMEDELTA_absolute(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func))
 {
     UNARY_LOOP {
@@ -1886,6 +1901,15 @@ NPY_NO_EXPORT void
 }
 
 NPY_NO_EXPORT void
+@TYPE@_positive(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func))
+{
+    UNARY_LOOP {
+        const @type@ in1 = *(@type@ *)ip1;
+        *((@type@ *)op1) = +in1;
+    }
+}
+
+NPY_NO_EXPORT void
 @TYPE@_sign(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func))
 {
     /* Sign of nan is nan */
@@ -2189,6 +2213,15 @@ HALF_negative(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUS
 }
 
 NPY_NO_EXPORT void
+HALF_positive(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func))
+{
+    UNARY_LOOP {
+        const npy_half in1 = *(npy_half *)ip1;
+        *((npy_half *)op1) = +in1;
+    }
+}
+
+NPY_NO_EXPORT void
 HALF_sign(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func))
 {
     /* Sign of nan is nan */
diff --git a/numpy/core/src/umath/loops.h.src b/numpy/core/src/umath/loops.h.src
index e5c0dc855..d20b776a0 100644
--- a/numpy/core/src/umath/loops.h.src
+++ b/numpy/core/src/umath/loops.h.src
@@ -61,6 +61,9 @@ BOOL__ones_like(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UN
 NPY_NO_EXPORT void
 @S@@TYPE@__ones_like(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(data));
 
+NPY_NO_EXPORT void
+@S@@TYPE@_positive(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func));
+
 /**begin repeat2
  * #isa = , _avx2#
  */
@@ -235,6 +238,8 @@ NPY_NO_EXPORT void
 NPY_NO_EXPORT void
 @TYPE@_negative(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func));
 
+NPY_NO_EXPORT void
+@TYPE@_positive(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func));
 
 NPY_NO_EXPORT void
 @TYPE@_sign(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func));
@@ -384,6 +389,9 @@ NPY_NO_EXPORT void
 TIMEDELTA_negative(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func));
 
 NPY_NO_EXPORT void
+TIMEDELTA_positive(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func));
+
+NPY_NO_EXPORT void
 TIMEDELTA_absolute(char **args, npy_intp *dimensions, npy_intp *steps, void *NPY_UNUSED(func));
 
 NPY_NO_EXPORT void
diff --git a/numpy/core/tests/test_datetime.py b/numpy/core/tests/test_datetime.py
index b5d096d47..12ebd5ae9 100644
--- a/numpy/core/tests/test_datetime.py
+++ b/numpy/core/tests/test_datetime.py
@@ -794,6 +794,12 @@ class TestDateTime(TestCase):
             assert_equal(np.negative(tdb), tda)
             assert_equal(np.negative(tdb).dtype, tda.dtype)
 
+            # positive ufunc
+            assert_equal(np.positive(tda), tda)
+            assert_equal(np.positive(tda).dtype, tda.dtype)
+            assert_equal(np.positive(tdb), tdb)
+            assert_equal(np.positive(tdb).dtype, tdb.dtype)
+
             # absolute ufunc
             assert_equal(np.absolute(tdb), tda)
             assert_equal(np.absolute(tdb).dtype, tda.dtype)
diff --git a/numpy/core/tests/test_half.py b/numpy/core/tests/test_half.py
index 56b574ae8..75b74f407 100644
--- a/numpy/core/tests/test_half.py
+++ b/numpy/core/tests/test_half.py
@@ -323,6 +323,7 @@ class TestHalf(TestCase):
         assert_equal(np.conjugate(b), b)
         assert_equal(np.absolute(b), [2, 5, 1, 4, 3])
         assert_equal(np.negative(b), [2, -5, -1, -4, -3])
+        assert_equal(np.positive(b), b)
         assert_equal(np.sign(b), [-1, 1, 1, 1, 1])
         assert_equal(np.modf(b), ([0, 0, 0, 0, 0], b))
         assert_equal(np.frexp(b), ([-0.5, 0.625, 0.5, 0.5, 0.75], [2, 3, 1, 3, 2]))
diff --git a/numpy/core/tests/test_umath.py b/numpy/core/tests/test_umath.py
index 41108ab5f..62882eaa9 100644
--- a/numpy/core/tests/test_umath.py
+++ b/numpy/core/tests/test_umath.py
@@ -1057,6 +1057,7 @@ class TestBool(TestCase):
     def test_exceptions(self):
         a = np.ones(1, dtype=np.bool_)
         assert_raises(TypeError, np.negative, a)
+        assert_raises(TypeError, np.positive, a)
         assert_raises(TypeError, np.subtract, a, a)
 
     def test_truth_table_logical(self):
@@ -1349,6 +1350,25 @@ class TestAbsoluteNegative(TestCase):
         np.abs(np.ones_like(d), out=d)
 
 
+class TestPositive(TestCase):
+    def test_valid(self):
+        valid_dtypes = [int, float, complex, object]
+        for dtype in valid_dtypes:
+            x = np.arange(5, dtype=dtype)
+            result = np.positive(x)
+            assert_equal(x, result, err_msg=str(dtype))
+
+    def test_invalid(self):
+        with assert_raises(TypeError):
+            np.positive(True)
+        with assert_raises(TypeError):
+            np.positive(np.datetime64('2000-01-01'))
+        with assert_raises(TypeError):
+            np.positive(np.array(['foo'], dtype=str))
+        with assert_raises(TypeError):
+            np.positive(np.array(['bar'], dtype=object))
+
+
 class TestSpecialMethods(TestCase):
     def test_wrap(self):