Fix astype

python/mxnet/ndarray/ndarray.py

@@ -2606,12 +2606,12 @@ def astype(self, dtype, copy=True):
         <type 'numpy.int32'>
         """
 
+        if dtype is None:
+            dtype = _np.float32
         if not copy and np.dtype(dtype) == self.dtype:
             return self
 
-        res = empty(self.shape, ctx=self.ctx, dtype=dtype)
-        self.copyto(res)
-        return res
+        return op.cast(self, dtype=dtype)
 
     def copyto(self, other):
         """Copies the value of this array to another array.

python/mxnet/ndarray/sparse.py

@@ -230,6 +230,7 @@ def astype(self, dtype, copy=True):
         if not copy and np.dtype(dtype) == self.dtype:
             return self
 
+        # Use copyto for casting, as op.cast(self, dtype=dtype) doesn't support sparse stype
         res = zeros(shape=self.shape, ctx=self.context,
                     dtype=dtype, stype=self.stype)
         self.copyto(res)

python/mxnet/numpy/multiarray.py

@@ -1247,12 +1247,12 @@ def astype(self, dtype, order='K', casting='unsafe', subok=True, copy=True):  #
             raise ValueError('casting must be equal to \'unsafe\'')
         if not subok:
             raise ValueError('subok must be equal to True')
+        if dtype is None:
+            dtype = _np.float32
         if not copy and _np.dtype(dtype) == self.dtype:
             return self
 
-        res = empty(self.shape, dtype=dtype, ctx=self.ctx)
-        self.copyto(res)
-        return res
+        return _npi.cast(self, dtype=dtype)
 
     def copyto(self, other):
         """Copies the value of this array to another array.

src/ndarray/ndarray.cc

@@ -2177,8 +2177,9 @@ bool CopyToType(const nnvm::NodeAttrs &attrs, std::vector<int> *in_attrs,
   CHECK_EQ(in_attrs->size(), 1U);
   CHECK_EQ(out_attrs->size(), 1U);
   int in_type = in_attrs->at(0);
-  int out_type = in_type;
-  TYPE_ASSIGN_CHECK(*out_attrs, 0, out_type);
+  if (out_attrs->at(0) == -1) {
+    TYPE_ASSIGN_CHECK(*out_attrs, 0, in_type);
+  }
   return out_attrs->at(0) != -1;
 }
 

tests/python/unittest/test_deferred_compute.py

@@ -260,6 +260,14 @@ def f(a, *, nd):
     _assert_dc(_dc_simple_setup, f)
 
 
+def test_dc_astype():
+    def f(a, *, nd):
+        a = a.astype(np.int32)
+        b = nd.zeros_like(a)
+        return [a + b]
+
+    _assert_dc(_dc_simple_setup, f)
+
 ###############################################################################
 # Gluon
 ###############################################################################