Add dtype argument to asarray

src/python/module/z5py/dataset.py

@@ -51,8 +51,16 @@ def __init__(self, dset_impl, handle, parent, name, n_threads=1):
         self._parent = parent
         self._name = name
 
-    def __array__(self):
-        return self[...]
+    def __array__(self, dtype=None):
+        """ Create a numpy array containing the whole dataset.
+
+        NOTE: Datasets are not interchangeble with arrays!
+        Every time this method is called the whole dataset is loaded into memory!
+        """
+        arr = self[...]
+        if dtype is not None:
+            arr = arr.astype(dtype, copy=False)
+        return arr
 
     @staticmethod
     def _to_zarr_compression_options(compression, compression_options):

src/python/test/test_asarray.py

@@ -1,5 +1,4 @@
 import unittest
-import pickle
 import sys
 from shutil import rmtree
 
@@ -15,13 +14,12 @@
 class TestAsarray(unittest.TestCase):
 
     def setUp(self):
-        sample_data = np.array([ [3, 4], [7, 8]])
+        self.sample_data = np.random.randint(0, 10000, size=(10, 10))
         self.test_fn = 'test.n5'
         self.test_ds = 'test'
         with z5py.File(self.test_fn, 'w') as zfh:
-            zfh.create_dataset(self.test_ds, data=sample_data)
+            zfh.create_dataset(self.test_ds, data=self.sample_data)
         self.ff = z5py.File(self.test_fn, 'r')
-
 
     def tearDown(self):
         try:
@@ -31,7 +29,9 @@ def tearDown(self):
 
     def test_asarray(self):
         uniques = np.unique(self.ff[self.test_ds])
-        self.assertEqual(len(uniques), 4)
+        expected = np.unique(self.sample_data)
+        self.assertTrue(np.array_equal(uniques, expected))
+
 
 if __name__ == '__main__':
     unittest.main()