Allow disabling filling of missing chunks

zarr/core.py

@@ -135,6 +135,7 @@ class Array:
     set_mask_selection
     get_coordinate_selection
     set_coordinate_selection
+    set_options
     digest
     hexdigest
     resize
@@ -191,6 +192,9 @@ def __init__(
         self._oindex = OIndex(self)
         self._vindex = VIndex(self)
 
+        # initialize options
+        self.set_options()
+
     def _load_metadata(self):
         """(Re)load metadata from store."""
         if self._synchronizer is None:
@@ -860,6 +864,8 @@ def _get_basic_selection_zd(self, selection, out=None, fields=None):
             cdata = self.chunk_store[ckey]
 
         except KeyError:
+            if not self._fill_missing_chunk:
+                raise
             # chunk not initialized
             chunk = np.zeros((), dtype=self._dtype)
             if self._fill_value is not None:
@@ -1547,6 +1553,18 @@ def set_coordinate_selection(self, selection, value, fields=None):
 
         self._set_selection(indexer, value, fields=fields)
 
+    def set_options(self, fill_missing_chunk=True):
+        """Set options.
+
+        Parameters
+        ----------
+        fill_missing_chunk : bool
+            Whether Zarr is supposed to fill missing chunks.  Defaults to True.
+
+        """
+
+        self._fill_missing_chunk = fill_missing_chunk
+
     def set_mask_selection(self, selection, value, fields=None):
         """Modify a selection of individual items, by providing a Boolean array of the
         same shape as the array against which the selection is being made, where True
@@ -1871,6 +1889,8 @@ def _chunk_getitem(self, chunk_coords, chunk_selection, out, out_selection,
             cdata = self.chunk_store[ckey]
 
         except KeyError:
+            if not self._fill_missing_chunk:
+                raise
             # chunk not initialized
             if self._fill_value is not None:
                 if fields:

zarr/tests/test_missing.py

@@ -0,0 +1,44 @@
+import unittest
+from zarr.creation import array
+
+
+class TestArrayMissingKeys(unittest.TestCase):
+    def test_raises_on_missing_key_zd(self):
+        a = array(1, chunks=1)
+
+        # pop first chunk
+        a.chunk_store.pop("0")
+
+        # read from missing chunk and make sure fill-value is returned
+        assert a.fill_value == a[()]
+
+        # configure raise on missing chunk
+        a.set_options(fill_missing_chunk=False)
+
+        # reading missing chunk should raise
+        with self.assertRaises(KeyError):
+            a[()]
+
+    def test_raises_on_missing_key_1d(self):
+        a = array(range(4), chunks=2)
+
+        # pop first chunk
+        a.chunk_store.pop("0")
+
+        # read from missing chunk and make sure fill-value is returned
+        assert a.fill_value == a[0]
+        assert a.fill_value == a[1]
+
+        # read from avaible chunk w/o error
+        assert 2 == a[2]
+        assert 3 == a[3]
+
+        # configure raise on missing chunk
+        a.set_options(fill_missing_chunk=False)
+
+        # reading missing chunk should raise
+        with self.assertRaises(KeyError):
+            a[0]
+
+        with self.assertRaises(KeyError):
+            a[:2]