Apply suggestions from code review

Co-authored-by: Erik van Sebille <erikvansebille@gmail.com>

parcels/particleset/particlesetnodes.py

@@ -419,7 +419,7 @@ def data_indices(self, variable_name, compare_values, invert=False):
         *not implemented*, as node-based data structure is _not_ index-based.
         Please use 'data_ids' or 'data_nodes'
         """
-        raise NotImplementedError("'data_indices' function shall not be used as the node-based structure is not indexable.")
+        raise NotImplementedError("'data_indices' function cannot be used as the node-based structure is not indexable.")
 
     def data_ids(self, variable_name, compare_values, invert=False):
         """Get the ID's of all particles where the value of
@@ -508,7 +508,7 @@ def populate_indices(self):
         Functionality:
         *not implemented*, as node-based data structure is _not_ index-based.
         """
-        raise NotImplementedError("'populate_indices' function shall not be used as the node-based structure is not indexable.")
+        raise NotImplementedError("'populate_indices' function cannot be used as the node-based structure is not indexable.")
 
     def cptr(self, index):
         return self._collection.cptr(index)

parcels/particleset/particlesetsoa.py

@@ -610,7 +610,7 @@ def split_by_index(self, indices):
         The reason for it can, for example, be that the set exceeds a pre-defined maximum number of elements, which for
         performance reasons mandates a split.
 
-        The function shall return the newly created or extended Particle collection, i.e. either the collection that
+        The function returns the newly created or extended Particle collection, i.e. either the collection that
         results from a collection split or this very collection, containing the newly-split particles.
         """
         super().split_by_index(indices)
@@ -632,7 +632,7 @@ def split_by_id(self, ids):
         The reason for it can, for example, be that the set exceeds a pre-defined maximum number of elements, which for
         performance reasons mandates a split.
 
-        The function shall return the newly created or extended Particle collection, i.e. either the collection that
+        The function returns the newly created or extended Particle collection, i.e. either the collection that
         results from a collection split or this very collection, containing the newly-split particles.
         """
         super().split_by_id(ids)