diff --git a/python/ql/lib/analysis/DefinitionTracking.qll b/python/ql/lib/analysis/DefinitionTracking.qll
index 0d58bd69b7b6..21155970375b 100644
--- a/python/ql/lib/analysis/DefinitionTracking.qll
+++ b/python/ql/lib/analysis/DefinitionTracking.qll
@@ -471,11 +471,10 @@ Definition getUniqueDefinition(Expr use) {
   not result = TLocalDefinition(use)
 }
 
-/** A helper class to get suitable locations for attributes */
-class NiceLocationExpr extends Expr {
-  /** Gets a textual representation of this element. */
-  override string toString() { result = this.(Expr).toString() }
+final class FinalExpr = Expr;
 
+/** A helper class to get suitable locations for attributes */
+class NiceLocationExpr extends FinalExpr {
   /**
    * Holds if this element is at the specified location.
    * The location spans column `bc` of line `bl` to
diff --git a/python/ql/lib/semmle/python/AstExtended.qll b/python/ql/lib/semmle/python/AstExtended.qll
index 9b6059dceae4..365b3989a022 100644
--- a/python/ql/lib/semmle/python/AstExtended.qll
+++ b/python/ql/lib/semmle/python/AstExtended.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 private import semmle.python.internal.CachedStages
 
diff --git a/python/ql/lib/semmle/python/AstGenerated.qll b/python/ql/lib/semmle/python/AstGenerated.qll
index e672cda001dd..3195095f6290 100644
--- a/python/ql/lib/semmle/python/AstGenerated.qll
+++ b/python/ql/lib/semmle/python/AstGenerated.qll
@@ -3,6 +3,8 @@
  *      WARNING: Any modifications to this file will be lost.
  *      Relations can be changed by modifying master.py.
  */
+overlay[local]
+module;
 
 import python
 
diff --git a/python/ql/lib/semmle/python/Class.qll b/python/ql/lib/semmle/python/Class.qll
index 19b81e86a125..cee0e730cb4f 100644
--- a/python/ql/lib/semmle/python/Class.qll
+++ b/python/ql/lib/semmle/python/Class.qll
@@ -1,6 +1,8 @@
 /**
  * Provides classes representing Python classes.
  */
+overlay[local]
+module;
 
 import python
 
diff --git a/python/ql/lib/semmle/python/Comment.qll b/python/ql/lib/semmle/python/Comment.qll
index 839d700b8cd1..c87ccc1521d2 100644
--- a/python/ql/lib/semmle/python/Comment.qll
+++ b/python/ql/lib/semmle/python/Comment.qll
@@ -1,6 +1,8 @@
 /**
  * Provides classes representing comments in Python.
  */
+overlay[local]
+module;
 
 import python
 
diff --git a/python/ql/lib/semmle/python/Comprehensions.qll b/python/ql/lib/semmle/python/Comprehensions.qll
index 37f07614282f..12e71e2d5d11 100644
--- a/python/ql/lib/semmle/python/Comprehensions.qll
+++ b/python/ql/lib/semmle/python/Comprehensions.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 
 /** The base class for list, set and dictionary comprehensions, and generator expressions. */
diff --git a/python/ql/lib/semmle/python/Constants.qll b/python/ql/lib/semmle/python/Constants.qll
index 03254a4bfd04..f86019c0256f 100644
--- a/python/ql/lib/semmle/python/Constants.qll
+++ b/python/ql/lib/semmle/python/Constants.qll
@@ -1,4 +1,6 @@
 /** Standard builtin types and modules */
+overlay[local]
+module;
 
 import python
 
diff --git a/python/ql/lib/semmle/python/Exprs.qll b/python/ql/lib/semmle/python/Exprs.qll
index c374863d684e..6ab9f8d8340d 100644
--- a/python/ql/lib/semmle/python/Exprs.qll
+++ b/python/ql/lib/semmle/python/Exprs.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 private import python
 private import semmle.python.internal.CachedStages
 
diff --git a/python/ql/lib/semmle/python/Files.qll b/python/ql/lib/semmle/python/Files.qll
index 2da0dd61f885..bb3c504654e7 100644
--- a/python/ql/lib/semmle/python/Files.qll
+++ b/python/ql/lib/semmle/python/Files.qll
@@ -1,4 +1,6 @@
 /** Provides classes for working with files and folders. */
+overlay[local]
+module;
 
 import python
 private import codeql.util.FileSystem
@@ -178,6 +180,7 @@ class Container extends Impl::Container {
 
   override Container getParentContainer() { result = super.getParentContainer() }
 
+  overlay[global]
   Container getChildContainer(string baseName) {
     result = this.getAChildContainer() and
     result.getBaseName() = baseName
diff --git a/python/ql/lib/semmle/python/Flow.qll b/python/ql/lib/semmle/python/Flow.qll
index 898cd566ab96..b29f9fd13839 100644
--- a/python/ql/lib/semmle/python/Flow.qll
+++ b/python/ql/lib/semmle/python/Flow.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 private import semmle.python.internal.CachedStages
 private import codeql.controlflow.BasicBlock as BB
diff --git a/python/ql/lib/semmle/python/Function.qll b/python/ql/lib/semmle/python/Function.qll
index e15d28d3a12b..c133275b8b78 100644
--- a/python/ql/lib/semmle/python/Function.qll
+++ b/python/ql/lib/semmle/python/Function.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 
 /**
diff --git a/python/ql/lib/semmle/python/GuardedControlFlow.qll b/python/ql/lib/semmle/python/GuardedControlFlow.qll
index 73ea183850af..3169e4d0c1ad 100644
--- a/python/ql/lib/semmle/python/GuardedControlFlow.qll
+++ b/python/ql/lib/semmle/python/GuardedControlFlow.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 
 /** A basic block which terminates in a condition, splitting the subsequent control flow */
diff --git a/python/ql/lib/semmle/python/Import.qll b/python/ql/lib/semmle/python/Import.qll
index c75ef9f0c918..e8a7facccad3 100644
--- a/python/ql/lib/semmle/python/Import.qll
+++ b/python/ql/lib/semmle/python/Import.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 private import semmle.python.types.Builtins
 private import semmle.python.internal.CachedStages
diff --git a/python/ql/lib/semmle/python/Keywords.qll b/python/ql/lib/semmle/python/Keywords.qll
index b7ecca528bb9..da7b582ef16b 100644
--- a/python/ql/lib/semmle/python/Keywords.qll
+++ b/python/ql/lib/semmle/python/Keywords.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 
 class KeyValuePair extends KeyValuePair_, DictDisplayItem {
diff --git a/python/ql/lib/semmle/python/Module.qll b/python/ql/lib/semmle/python/Module.qll
index f22f0d6fe39f..a30aab452c38 100644
--- a/python/ql/lib/semmle/python/Module.qll
+++ b/python/ql/lib/semmle/python/Module.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 private import semmle.python.internal.CachedStages
 
diff --git a/python/ql/lib/semmle/python/Operations.qll b/python/ql/lib/semmle/python/Operations.qll
index e8f5e4799a54..c6318af63e25 100644
--- a/python/ql/lib/semmle/python/Operations.qll
+++ b/python/ql/lib/semmle/python/Operations.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 
 /** The base class for operators */
diff --git a/python/ql/lib/semmle/python/Patterns.qll b/python/ql/lib/semmle/python/Patterns.qll
index 9b4760611d00..fb99a123584e 100644
--- a/python/ql/lib/semmle/python/Patterns.qll
+++ b/python/ql/lib/semmle/python/Patterns.qll
@@ -1,6 +1,8 @@
 /**
  * Wrapping generated AST classes: `Pattern_` and subclasses.
  */
+overlay[local]
+module;
 
 import python
 
diff --git a/python/ql/lib/semmle/python/SSA.qll b/python/ql/lib/semmle/python/SSA.qll
index b71bd95de795..777792877340 100644
--- a/python/ql/lib/semmle/python/SSA.qll
+++ b/python/ql/lib/semmle/python/SSA.qll
@@ -1,4 +1,6 @@
 /** SSA library */
+overlay[local]
+module;
 
 import python
 
diff --git a/python/ql/lib/semmle/python/Scope.qll b/python/ql/lib/semmle/python/Scope.qll
index 4131455299cb..66a7170aec77 100644
--- a/python/ql/lib/semmle/python/Scope.qll
+++ b/python/ql/lib/semmle/python/Scope.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 private import semmle.python.dataflow.new.internal.ImportResolution
 
@@ -6,6 +9,7 @@ private import semmle.python.dataflow.new.internal.ImportResolution
  *
  * This aims to be the same as m.getAnExport(), but without using the points-to machinery.
  */
+overlay[global]
 private string getAModuleExport(Module m) {
   py_exports(m, result)
   or
@@ -76,6 +80,7 @@ class Scope extends Scope_ {
   predicate isTopLevel() { this.getEnclosingModule() = this.getEnclosingScope() }
 
   /** Holds if this scope is deemed to be public */
+  overlay[global]
   predicate isPublic() {
     /* Not inside a function */
     not this.getEnclosingScope() instanceof Function and
diff --git a/python/ql/lib/semmle/python/Stmts.qll b/python/ql/lib/semmle/python/Stmts.qll
index ea309227af67..c0dfac10ee84 100644
--- a/python/ql/lib/semmle/python/Stmts.qll
+++ b/python/ql/lib/semmle/python/Stmts.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 
 /** A statement */
diff --git a/python/ql/lib/semmle/python/Variables.qll b/python/ql/lib/semmle/python/Variables.qll
index 1249fd020caa..d2baf04a5bf1 100644
--- a/python/ql/lib/semmle/python/Variables.qll
+++ b/python/ql/lib/semmle/python/Variables.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 
 /** A variable, either a global or local variable (including parameters) */
diff --git a/python/ql/lib/semmle/python/essa/Definitions.qll b/python/ql/lib/semmle/python/essa/Definitions.qll
index aca6991b9f69..6e7b8d5b376a 100644
--- a/python/ql/lib/semmle/python/essa/Definitions.qll
+++ b/python/ql/lib/semmle/python/essa/Definitions.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 /*
  * Classification of variables. These should be non-overlapping and complete.
diff --git a/python/ql/lib/semmle/python/essa/Essa.qll b/python/ql/lib/semmle/python/essa/Essa.qll
index 384bfd2f91fe..ebc22beedf33 100644
--- a/python/ql/lib/semmle/python/essa/Essa.qll
+++ b/python/ql/lib/semmle/python/essa/Essa.qll
@@ -1,6 +1,8 @@
 /**
  * Library for SSA representation (Static Single Assignment form).
  */
+overlay[local]
+module;
 
 import python
 private import SsaCompute
diff --git a/python/ql/lib/semmle/python/essa/SsaCompute.qll b/python/ql/lib/semmle/python/essa/SsaCompute.qll
index d2512eecdede..fb030b6250ee 100644
--- a/python/ql/lib/semmle/python/essa/SsaCompute.qll
+++ b/python/ql/lib/semmle/python/essa/SsaCompute.qll
@@ -88,6 +88,8 @@
  * ```
  * and thus it falls out that `g3` must be `1`.
  */
+overlay[local]
+module;
 
 import python
 private import semmle.python.internal.CachedStages
diff --git a/python/ql/lib/semmle/python/essa/SsaDefinitions.qll b/python/ql/lib/semmle/python/essa/SsaDefinitions.qll
index 6c87af102fa9..827bee34474e 100644
--- a/python/ql/lib/semmle/python/essa/SsaDefinitions.qll
+++ b/python/ql/lib/semmle/python/essa/SsaDefinitions.qll
@@ -2,6 +2,8 @@
  * Provides classes and predicates for determining the uses and definitions of
  * variables for ESSA form.
  */
+overlay[local]
+module;
 
 import python
 private import semmle.python.internal.CachedStages
diff --git a/python/ql/lib/semmle/python/internal/CachedStages.qll b/python/ql/lib/semmle/python/internal/CachedStages.qll
index 687cabeceaed..df96e8498556 100644
--- a/python/ql/lib/semmle/python/internal/CachedStages.qll
+++ b/python/ql/lib/semmle/python/internal/CachedStages.qll
@@ -35,6 +35,7 @@ module Stages {
    * Computes predicates based on the AST.
    * These include SSA and basic-blocks.
    */
+  overlay[local]
   cached
   module AST {
     /**
diff --git a/python/ql/lib/semmle/python/types/Builtins.qll b/python/ql/lib/semmle/python/types/Builtins.qll
index 796397f72cd6..371cf758d5c5 100644
--- a/python/ql/lib/semmle/python/types/Builtins.qll
+++ b/python/ql/lib/semmle/python/types/Builtins.qll
@@ -1,3 +1,6 @@
+overlay[local?]
+module;
+
 import python
 private import LegacyPointsTo
 
diff --git a/python/ql/lib/semmle/python/types/ImportTime.qll b/python/ql/lib/semmle/python/types/ImportTime.qll
index 1604013d7ff4..27f70b09aa40 100644
--- a/python/ql/lib/semmle/python/types/ImportTime.qll
+++ b/python/ql/lib/semmle/python/types/ImportTime.qll
@@ -1,3 +1,6 @@
+overlay[local]
+module;
+
 import python
 
 /**
diff --git a/python/ql/src/Variables/LoopVariableCapture/LoopVariableCaptureQuery.qll b/python/ql/src/Variables/LoopVariableCapture/LoopVariableCaptureQuery.qll
index 7f25701cac8e..987740236f24 100644
--- a/python/ql/src/Variables/LoopVariableCapture/LoopVariableCaptureQuery.qll
+++ b/python/ql/src/Variables/LoopVariableCapture/LoopVariableCaptureQuery.qll
@@ -3,8 +3,10 @@
 import python
 import semmle.python.dataflow.new.DataFlow
 
+final class FinalAstNode = AstNode;
+
 /** A looping construct. */
-abstract class Loop extends AstNode {
+abstract class Loop extends FinalAstNode {
   /**
    * Gets a loop variable of this loop.
    * For example, `x` and `y` in `for x,y in pairs: print(x+y)`
@@ -13,9 +15,9 @@ abstract class Loop extends AstNode {
 }
 
 /** A `for` loop. */
-private class ForLoop extends Loop, For {
+private class ForLoop extends Loop instanceof For {
   override Variable getALoopVariable() {
-    this.getTarget() = result.getAnAccess().getParentNode*() and
+    this.(For).getTarget() = result.getAnAccess().getParentNode*() and
     result.getScope() = this.getScope()
   }
 }
diff --git a/python/ql/src/analysis/ImportFailure.ql b/python/ql/src/analysis/ImportFailure.ql
index c9289a8b474a..71967e6e04f7 100644
--- a/python/ql/src/analysis/ImportFailure.ql
+++ b/python/ql/src/analysis/ImportFailure.ql
@@ -59,7 +59,9 @@ predicate ok_to_fail(ImportExpr ie) {
   os_specific_import(ie) != get_os()
 }
 
-class VersionTest extends ControlFlowNode {
+final class FinalControlFlowNode = ControlFlowNode;
+
+class VersionTest extends FinalControlFlowNode {
   VersionTest() {
     exists(string name |
       name.matches("%version%") and
@@ -70,7 +72,7 @@ class VersionTest extends ControlFlowNode {
     )
   }
 
-  override string toString() { result = "VersionTest" }
+  string toString() { result = "VersionTest" }
 }
 
 /** A guard on the version of the Python interpreter */