Comment typo fixes

Lib/compiler/ast.py

@@ -283,7 +283,7 @@ class Module(Node):
         return "Module(%s, %s)" % (repr(self.doc), repr(self.node))
 
 class Expression(Node):
-    # Expression is an artifical node class to support "eval"
+    # Expression is an artificial node class to support "eval"
     nodes["expression"] = "Expression"
     def __init__(self, node):
         self.node = node

Lib/compiler/visitor.py

@@ -66,7 +66,7 @@ class ExampleASTVisitor(ASTVisitor):
     """Prints examples of the nodes that aren't visited
 
     This visitor-driver is only useful for development, when it's
-    helpful to develop a visitor incremently, and get feedback on what
+    helpful to develop a visitor incrementally, and get feedback on what
     you still have to do.
     """
     examples = {}