Python: Address review comments.

Author: tausbn

python/ql/src/semmle/python/Stmts.qll

@@ -90,10 +90,16 @@ class AugAssign extends AugAssign_ {
     /* syntax: Expr += Expr */
     override Expr getASubExpression() { result = this.getOperation() }
 
-    /** Gets the target of this augmented assignment statement. */
+    /**
+     * Gets the target of this augmented assignment statement.
+     * That is, the `a` in `a += b`.
+     */
     Expr getTarget() { result = this.getOperation().(BinaryExpr).getLeft() }
 
-    /** Gets the value of this augmented assignment statement. */
+    /**
+     * Gets the value of this augmented assignment statement.
+     * That is, the `b` in `a += b`.
+     */
     Expr getValue() { result = this.getOperation().(BinaryExpr).getRight() }
 
     override Stmt getASubStatement() { none() }
@@ -426,6 +432,6 @@ class StmtList extends StmtList_ {
         exists(Stmt item | item = this.getAnItem() | item = a or item.contains(a))
     }
 
-    /** Gets the last item in this list of statements. */
+    /** Gets the last item in this list of statements, if any. */
     Stmt getLastItem() { result = this.getItem(max(int i | exists(this.getItem(i)))) }
 }