Add magic method abs to NDArray and Symbol.

python/mxnet/ndarray/ndarray.py

@@ -205,6 +205,10 @@ def _to_shared_mem(self):
             self.handle, ctypes.byref(shared_pid), ctypes.byref(shared_id)))
         return shared_pid.value, shared_id.value, self.shape, self.dtype
 
+    def __abs__(self):
+        """x.__abs__() <=> abs(x) <=> x.abs() <=> mx.nd.abs(x, y)"""
+        return self.abs()
+
     def __add__(self, other):
         """x.__add__(y) <=> x+y <=> mx.nd.add(x, y) """
         return add(self, other)

tests/python/unittest/test_ndarray.py

@@ -172,6 +172,15 @@ def test_ndarray_negate():
     assert_almost_equal(npy, arr.asnumpy())
 
 
+@with_seed()
+def test_ndarray_magic_abs():
+    for dim in range(1, 7):
+        shape = rand_shape_nd(dim)
+        npy = np.random.uniform(-10, 10, shape)
+        arr = mx.nd.array(npy)
+        assert_almost_equal(abs(arr).asnumpy(), arr.abs().asnumpy())
+
+
 @with_seed()
 def test_ndarray_reshape():
     tensor = (mx.nd.arange(30) + 1).reshape(2, 3, 5)