diff --git a/pkgs/development/interpreters/python/build-python-package.nix b/pkgs/development/interpreters/python/build-python-package.nix
index 982542c1fc3..12d17b2e832 100644
--- a/pkgs/development/interpreters/python/build-python-package.nix
+++ b/pkgs/development/interpreters/python/build-python-package.nix
@@ -7,7 +7,7 @@
 , setuptools
 , unzip
 , ensureNewerSourcesHook
-, pythonModule
+, toPythonModule
 , namePrefix
 , bootstrapped-pip
 , flit
@@ -19,7 +19,7 @@ let
   wheel-specific = import ./build-python-package-wheel.nix { };
   common = import ./build-python-package-common.nix { inherit python bootstrapped-pip; };
   mkPythonDerivation = import ./mk-python-derivation.nix {
-    inherit lib python wrapPython setuptools unzip ensureNewerSourcesHook pythonModule namePrefix;
+    inherit lib python wrapPython setuptools unzip ensureNewerSourcesHook toPythonModule namePrefix;
   };
 in
 
diff --git a/pkgs/development/interpreters/python/mk-python-derivation.nix b/pkgs/development/interpreters/python/mk-python-derivation.nix
index 1fd6745093b..5f7348ac825 100644
--- a/pkgs/development/interpreters/python/mk-python-derivation.nix
+++ b/pkgs/development/interpreters/python/mk-python-derivation.nix
@@ -7,7 +7,7 @@
 , unzip
 , ensureNewerSourcesHook
 # Whether the derivation provides a Python module or not.
-, pythonModule
+, toPythonModule
 , namePrefix
 }:
 
@@ -60,7 +60,7 @@ if disabled
 then throw "${name} not supported for interpreter ${python.executable}"
 else
 
-python.stdenv.mkDerivation (builtins.removeAttrs attrs [
+toPythonModule (python.stdenv.mkDerivation (builtins.removeAttrs attrs [
     "disabled" "checkInputs" "doCheck" "doInstallCheck" "dontWrapPythonPrograms" "catchConflicts"
   ] // {
 
@@ -95,14 +95,9 @@ python.stdenv.mkDerivation (builtins.removeAttrs attrs [
     ${python.interpreter} ${./catch_conflicts}/catch_conflicts.py
   '' + attrs.postFixup or '''';
 
-  passthru = {
-    inherit python; # The python interpreter
-    inherit pythonModule;
-  } // passthru;
-
   meta = {
     # default to python's platforms
     platforms = python.meta.platforms;
     isBuildPythonPackage = python.meta.platforms;
   } // meta;
-})
+}))
diff --git a/pkgs/top-level/python-packages.nix b/pkgs/top-level/python-packages.nix
index 5b10697deb4..d47d95aee90 100644
--- a/pkgs/top-level/python-packages.nix
+++ b/pkgs/top-level/python-packages.nix
@@ -56,14 +56,14 @@ let
     flit = self.flit;
     # We want Python libraries to be named like e.g. "python3.6-${name}"
     inherit namePrefix;
-    pythonModule = python;
+    inherit toPythonModule;
   }));
 
   buildPythonApplication = makeOverridablePythonPackage ( makeOverridable (callPackage ../development/interpreters/python/build-python-package.nix {
     inherit bootstrapped-pip;
     flit = self.flit;
     namePrefix = "";
-    pythonModule = false;
+    toPythonModule = x: x; # Application does not provide modules.
   }));
 
   graphiteVersion = "1.0.2";
@@ -87,15 +87,12 @@ let
     in fetcher (builtins.removeAttrs attrs ["format"]) );
 
   # Check whether a derivation provides a Python module.
-  hasPythonModule = drv: (hasAttr "pythonModule" drv) && ( (getAttr "pythonModule" drv) == python);
+  hasPythonModule = drv: drv?pythonModule && drv.pythonModule == python;
 
   # Get list of required Python modules given a list of derivations.
   requiredPythonModules = drvs: let
-    filterNull = list: filter (x: !isNull x) list;
-    conditionalGetRecurse = attr: condition: drv: let f = conditionalGetRecurse attr condition; in
-      (if (condition drv) then unique [drv]++(concatMap f (filterNull(getAttr attr drv))) else []);
-    _required = drv: conditionalGetRecurse "propagatedBuildInputs" hasPythonModule drv;
-  in [python] ++ (unique (concatMap _required (filterNull drvs)));
+    modules = filter hasPythonModule drvs;
+  in unique ([python] ++ modules ++ concatLists (catAttrs "requiredPythonModules" modules));
 
   # Create a PYTHONPATH from a list of derivations. This function recurses into the items to find derivations
   # providing Python modules.
@@ -106,9 +103,9 @@ let
     drv.overrideAttrs( oldAttrs: {
       # Use passthru in order to prevent rebuilds when possible.
       passthru = (oldAttrs.passthru or {})// {
-        name = namePrefix + oldAttrs.name;
         pythonModule = python;
         pythonPath = [ ]; # Deprecated, for compatibility.
+        requiredPythonModules = requiredPythonModules drv.propagatedBuildInputs;
       };
     });
 
@@ -129,7 +126,7 @@ in {
 
   recursivePthLoader = callPackage ../development/python-modules/recursive-pth-loader { };
 
-  setuptools = callPackage ../development/python-modules/setuptools { };
+  setuptools = toPythonModule (callPackage ../development/python-modules/setuptools { });
 
   vowpalwabbit = callPackage ../development/python-modules/vowpalwabbit {
     pythonPackages = self;