Merge pull request #1225 from jmishra01/memory-efficient

Use generator instead of list expand or add method

lark/tree.py

@@ -68,17 +68,16 @@ def _pretty_label(self):
         return self.data
 
     def _pretty(self, level, indent_str):
+        yield f'{indent_str*level}{self._pretty_label()}'
         if len(self.children) == 1 and not isinstance(self.children[0], Tree):
-            return [indent_str*level, self._pretty_label(), '\t', '%s' % (self.children[0],), '\n']
-
-        l = [indent_str*level, self._pretty_label(), '\n']
-        for n in self.children:
-            if isinstance(n, Tree):
-                l += n._pretty(level+1, indent_str)
-            else:
-                l += [indent_str*(level+1), '%s' % (n,), '\n']
-
-        return l
+            yield f'\t{self.children[0]}\n'
+        else:
+            yield '\n'
+            for n in self.children:
+                if isinstance(n, Tree):
+                    yield from n._pretty(level+1, indent_str)
+                else:
+                    yield f'{indent_str*(level+1)}{n}\n'
 
     def pretty(self, indent_str: str='  ') -> str:
         """Returns an indented string representation of the tree.
@@ -149,13 +148,15 @@ def iter_subtrees_topdown(self):
         Iterates over all the subtrees, return nodes in order like pretty() does.
         """
         stack = [self]
+        stack_append = stack.append
+        stack_pop = stack.pop
         while stack:
-            node = stack.pop()
+            node = stack_pop()
             if not isinstance(node, Tree):
                 continue
             yield node
             for child in reversed(node.children):
-                stack.append(child)
+                stack_append(child)
 
     def find_pred(self, pred: 'Callable[[Tree[_Leaf_T]], bool]') -> 'Iterator[Tree[_Leaf_T]]':
         """Returns all nodes of the tree that evaluate pred(node) as true."""