compiler: Simplify implementation and polish docstrings

Author: FabioLuporini

devito/ir/clusters/cluster.py

@@ -177,15 +177,15 @@ def exprs_dimensions(self):
         The Dimensions that appear explicitly in the Cluster expressions.
         """
         dims_explicit = {i for i in self.free_symbols if i.is_Dimension}
-        dims_implicit = set().union(*[set(e.implicit_dims) for e in self.exprs])
+        dims_implicit = {d for e in self.exprs for d in e.implicit_dims}
         return dims_explicit | dims_implicit
 
     @cached_property
     def guards_dimensions(self):
         """
         The Dimensions that appear explicitly in the Cluster guards.
         """
-        syms_guards = set().union(*[e.free_symbols for e in self.guards.values()])
+        syms_guards = {d for e in self.guards.values() for d in e.free_symbols}
         dims_guards = {i for i in syms_guards if i.is_Dimension}
         return dims_guards
 

devito/symbolics/extended_sympy.py

@@ -151,9 +151,8 @@ def __mul__(self, other):
 class Terminal:
 
     """
-    Abstract base class for all terminal objects, that is, those objects
-    collected by `retrieve_terminals` in addition to all other SymPy atoms
-    such as `Symbol`, `Number`, etc.
+    Abstract base class for special SymPy objects that can only appear as
+    leaves (that is nodes with no children/arguments) in an expression.
     """
 
     pass
@@ -553,10 +552,6 @@ class Reserved(Pickable):
     """
     A base class for all reserved words used throughout the lowering process,
     including the final stage of code generation itself.
-
-    Reserved objects have the following properties:
-
-        * `estimate_cost(o) = 0`, where `o` is an instance of Reserved
     """
 
     pass