diff --git a/pkgs/development/interpreters/python/default.nix b/pkgs/development/interpreters/python/default.nix
index bb5c3b3a97f5..f1461d784be0 100644
--- a/pkgs/development/interpreters/python/default.nix
+++ b/pkgs/development/interpreters/python/default.nix
@@ -27,7 +27,9 @@ with pkgs;
         isPy35 = pythonVersion == "3.5";
         isPy36 = pythonVersion == "3.6";
         isPy37 = pythonVersion == "3.7";
-        isPy3k = lib.strings.substring 0 1 pythonVersion == "3";
+        isPy2 = lib.strings.substring 0 1 pythonVersion == "2";
+        isPy3 = lib.strings.substring 0 1 pythonVersion == "3";
+        isPy3k = isPy3;
         isPyPy = interpreter == "pypy";
 
         buildEnv = callPackage ./wrapper.nix { python = self; inherit (pythonPackages) requiredPythonModules; };
diff --git a/pkgs/development/python-modules/matplotlib/2.nix b/pkgs/development/python-modules/matplotlib/2.nix
index dec34c64f0a5..129b864a241d 100644
--- a/pkgs/development/python-modules/matplotlib/2.nix
+++ b/pkgs/development/python-modules/matplotlib/2.nix
@@ -45,7 +45,7 @@ buildPythonPackage rec {
     ++ stdenv.lib.optionals enableGtk3 [ cairo pycairo gtk3 gobject-introspection pygobject3 ]
     ++ stdenv.lib.optionals enableTk [ tcl tk tkinter libX11 ]
     ++ stdenv.lib.optionals enableQt [ pyqt4 ]
-    ++ stdenv.lib.optionals (builtins.hasAttr "isPy2" python) [ functools32 subprocess32 ];
+    ++ stdenv.lib.optionals python.isPy2 [ functools32 subprocess32 ];
 
   patches =
     [ ./basedirlist.patch ] ++
diff --git a/pkgs/servers/uwsgi/default.nix b/pkgs/servers/uwsgi/default.nix
index 074b19724d28..91053019ac12 100644
--- a/pkgs/servers/uwsgi/default.nix
+++ b/pkgs/servers/uwsgi/default.nix
@@ -7,7 +7,7 @@
 , ruby, php-embed, mysql
 }:
 
-let pythonPlugin = pkg : lib.nameValuePair "python${if pkg ? isPy2 then "2" else "3"}" {
+let pythonPlugin = pkg : lib.nameValuePair "python${if pkg.isPy2 then "2" else "3"}" {
                            interpreter = pkg.interpreter;
                            path = "plugins/python";
                            inputs = [ pkg ncurses ];