Support dtype= and copy= arguments in __array__(), as required by num…

…py 2. (#64)

src/delayedarray/DelayedArray.py

@@ -156,15 +156,36 @@ def __repr__(self) -> str:
         return preamble + "\n" + converted
 
     # For NumPy:
-    def __array__(self) -> ndarray:
+    def __array__(self, dtype: Optional[numpy.dtype] = None, copy: bool = True) -> ndarray:
         """Convert a ``DelayedArray`` to a NumPy array, to be used by
         :py:meth:`~numpy.array`. 
 
+        Args:
+            dtype:
+                The desired NumPy type of the output array. If None, the
+                type of the seed is used.
+
+            copy:
+                Currently ignored. The output is never a reference to the
+                underlying seed, even if the seed is another NumPy array.
+
         Returns:
             NumPy array of the same type as :py:attr:`~dtype` and shape as
-            :py:attr:`~shape`. 
+            :py:attr:`~shape`.
         """
-        return to_dense_array(self._seed)
+        if dtype is None or dtype == self.dtype:
+            return to_dense_array(self._seed)
+        else:
+            # Filling it chunk by chunk rather than doing a big coercion,
+            # to avoid creating an unnecessary intermediate full matrix.
+            output = numpy.ndarray(self.shape, dtype=dtype)
+            if is_masked(self._seed):
+                output = numpy.ma.array(output, mask=False)
+            def fill_output(job, part):
+                subsets = (*(slice(s, e) for s, e in job),)
+                output[subsets] = part
+            apply_over_blocks(self._seed, fill_output)
+            return output
 
     def __array_ufunc__(self, ufunc, method, *inputs, **kwargs) -> "DelayedArray":
         """Interface with NumPy array methods. This is used to implement

src/delayedarray/SparseNdarray.py

@@ -210,15 +210,24 @@ def __repr__(self) -> str:
 
 
     # For NumPy:
-    def __array__(self) -> numpy.ndarray:
+    def __array__(self, dtype: Optional[numpy.dtype] = None, copy: bool = True) -> numpy.ndarray:
         """Convert a ``SparseNdarray`` to a NumPy array.
 
+        Args:
+            dtype:
+                The desired NumPy type of the output array. If None, the
+                type of the seed is used.
+
+            copy:
+                Currently ignored. The output is never a reference to the
+                underlying seed, even if the seed is another NumPy array.
+
         Returns:
             Dense array of the same type as :py:attr:`~dtype` and shape as
             :py:attr:`~shape`.
         """
         indices = _spawn_indices(self._shape)
-        return _extract_dense_array_from_SparseNdarray(self, indices)
+        return _extract_dense_array_from_SparseNdarray(self, indices, dtype=dtype)
 
     # Assorted dunder methods.
     def __add__(self, other) -> Union["SparseNdarray", numpy.ndarray]:
@@ -1231,18 +1240,20 @@ def _recursive_extract_dense_array(contents: numpy.ndarray, subset: Tuple[Sequen
             pos += 1
 
 
-def _extract_dense_array_from_SparseNdarray(x: SparseNdarray, subset: Tuple[Sequence[int], ...]) -> numpy.ndarray:
+def _extract_dense_array_from_SparseNdarray(x: SparseNdarray, subset: Tuple[Sequence[int], ...], dtype: Optional[numpy.dtype] = None) -> numpy.ndarray:
     idims = [len(y) for y in subset]
     subset_summary = _characterize_indices(subset[0], x._shape[0])
 
     # We reverse the dimensions so that we use F-contiguous storage. This also
     # makes it slightly easier to do the recursion as we can just index by
     # the first dimension to obtain a subarray at each recursive step. 
-    output = numpy.zeros((*reversed(idims),), dtype=x._dtype)
+    if dtype is None:
+        dtype = x._dtype
+    output = numpy.zeros((*reversed(idims),), dtype=dtype)
+    if x._is_masked:
+        output = numpy.ma.MaskedArray(output, mask=False)
 
     if x._contents is not None:
-        if x._is_masked:
-            output = numpy.ma.MaskedArray(output, mask=False)
         ndim = len(x._shape)
         if ndim > 1:
             _recursive_extract_dense_array(x._contents, subset, subset_summary=subset_summary, output=output, dim=ndim-1)

tests/test_DelayedArray.py

@@ -18,6 +18,12 @@ def test_DelayedArray_dense():
 
     dump = numpy.array(x)
     assert isinstance(dump, numpy.ndarray)
+    assert dump.dtype == x.dtype
+    assert (dump == raw).all()
+
+    dump = numpy.array(x, dtype=numpy.float64)
+    assert isinstance(dump, numpy.ndarray)
+    assert dump.dtype == numpy.float64
     assert (dump == raw).all()
 
 
@@ -69,6 +75,16 @@ def test_DelayedArray_masked():
     x = delayedarray.wrap(y)
     assert delayedarray.is_masked(x)
 
+    dump = numpy.array(x)
+    assert isinstance(dump, numpy.ndarray)
+    assert dump.dtype == x.dtype
+    assert (dump == numpy.array(y)).all()
+
+    dump = numpy.array(x, dtype=numpy.float32)
+    assert isinstance(dump, numpy.ndarray)
+    assert dump.dtype == numpy.float32
+    assert (dump == numpy.array(y, dtype=numpy.float32)).all()
+
 
 #######################################################
 #######################################################
@@ -356,4 +372,4 @@ def test_SparseNdarray_all_sparse(mask_rate, buffer_size):
 
     # Zero-length array is respected.
     y = delayedarray.wrap(delayedarray.SparseNdarray((0,), None, dtype=numpy.int32, index_dtype=numpy.int32)) * 50
-    assert y.all()
+    assert y.all()

tests/test_SparseNdarray.py

@@ -188,6 +188,8 @@ def test_SparseNdarray_extract_dense_array_3d(mask_rate):
     # Full extraction.
     output = delayedarray.to_dense_array(y)
     assert_identical_ndarrays(output, convert_SparseNdarray_to_numpy(y))
+    assert_identical_ndarrays(numpy.array(output), numpy.array(y))
+    assert_identical_ndarrays(numpy.array(output, dtype=numpy.int32), numpy.array(y, dtype=numpy.int32))
 
     # Sliced extraction.
     slices = (slice(2, 15, 3), slice(0, 20, 2), slice(4, 8))