Correct deletion when reassigning a dsarray

dislib/classification/knn/base.py

@@ -53,7 +53,7 @@ class KNeighborsClassifier(BaseEstimator):
        but different labels, the results will depend on the ordering of the
        training data.
     https://en.wikipedia.org/wiki/K-nearest_neighbor_algorithm
-    
+
     Examples
     --------
     >>> import dislib as ds

dislib/data/array.py

@@ -12,6 +12,7 @@
 from scipy.sparse import issparse, csr_matrix
 from sklearn.utils import check_random_state
 import math
+import sys
 
 
 class Array(object):
@@ -73,8 +74,10 @@ def __init__(self, blocks, top_left_shape, reg_shape, shape, sparse,
 
     def __del__(self):
         if self._delete:
-            [compss_delete_object(b) for r_block in self._blocks for b in
-             r_block]
+            for r_block in self._blocks:
+                for b in r_block:
+                    if sys.getrefcount(b) <= 3:
+                        compss_delete_object(b)
 
     def __str__(self):
         return "ds-array(blocks=(...), top_left_shape=%r, reg_shape=%r, " \