fix linter

pystencils/gpu/indexing.py

@@ -42,6 +42,9 @@ class AbstractIndexing(abc.ABC):
     """
 
     def __init__(self, iteration_space: Tuple[slice], data_layout: Tuple):
+        for iter_space in iteration_space:
+            assert isinstance(iter_space, slice), f"iteration_space must be of type Tuple[slice], " \
+                                                  f"not tuple of type {type(iter_space)}"
         self._iteration_space = iteration_space
         self._data_layout = data_layout
         self._dim = len(iteration_space)
@@ -270,7 +273,7 @@ class LineIndexing(AbstractIndexing):
         data_layout: tuple to determine the fast and slow coordinates.
     """
 
-    def __init__(self,  iteration_space: Tuple[slice], data_layout: Tuple):
+    def __init__(self, iteration_space: Tuple[slice], data_layout: Tuple):
         super(LineIndexing, self).__init__(iteration_space, data_layout)
 
         if len(iteration_space) > 4: