pythonPackages.dnspython: use 1.x for Python 2

pkgs/applications/misc/electrum/default.nix

@@ -25,13 +25,7 @@ let
   # use the latest 1.x release instead
   py = python3.override {
     packageOverrides = self: super: {
-      dnspython = super.dnspython.overridePythonAttrs (oldAttrs: rec {
-        version = "1.16.0";
-        src = oldAttrs.src.override {
-          inherit version;
-          sha256 = "36c5e8e38d4369a08b6780b7f27d790a292b2b08eea01607865bf0936c558e01";
-        };
-      });
+      dnspython = super.dnspython_1;
     };
   };
 

pkgs/top-level/python-packages.nix

@@ -1694,7 +1694,13 @@ in {
 
   dnslib = callPackage ../development/python-modules/dnslib { };
 
-  dnspython = callPackage ../development/python-modules/dnspython { };
+  dnspython = if isPy3k then
+    callPackage ../development/python-modules/dnspython { }
+  else
+    self.dnspython_1;
+
+  dnspython_1 = callPackage ../development/python-modules/dnspython/1.nix { };
+
   dns = self.dnspython; # Alias for compatibility, 2017-12-10
 
   doc8 = callPackage ../development/python-modules/doc8 { };