anchor.diff:    pkgs = (import <nixpkgs> { }).overridePackages (pkgs: self: {
       # Upstream PR: https://github.com/NixOS/nixpkgs/pull/20590
       python3Packages = self.python3Packages // {
  -      flask = self.python3Packages.buildPythonPackage {
  +      flask = pkgs.python3Packages.buildPythonPackage {
           name = "flask-0.11.1";
   
           src = pkgs.fetchurl {
  
positive.code:           license = licenses.bsd3;
          };
        };
      };
    });
  
  
negative.code:   propagatedBuildInputs = [
      pkgs.python3Packages.flask
      pkgs.python3Packages.flask_login
      pkgs.python3Packages.flask_restful
    ];
  }
  