use python3 instead of python2

base16.nix

@@ -34,7 +34,7 @@ let
   # a transformation of this data such as rgb. The hacky python script pre-
   # processes the theme file in this way for consumption by the mustache
   # engine below.
-  python = pkgs.python.withPackages (ps: [ ps.pyyaml ]);
+  python = pkgs.python3.withPackages (ps: [ ps.pyyaml ]);
   preprocess = src:
     pkgs.stdenv.mkDerivation {
       name = "yaml";

base16writer.py

@@ -2,9 +2,9 @@
 import yaml
 import json
 import sys
-input = yaml.load(sys.stdin)
+input = yaml.safe_load(sys.stdin)
 input["colors"] = {}
-for (k,v) in input.copy().items():
+for (k,v) in list(input.copy().items()):
     if k[0:4] == "base":
         col = k[4:]
         input["colors"][k[4:]] = {