anchor.diff:  
       export PYTHONPATH="$out/lib/${python.libPrefix}/site-packages:$PYTHONPATH"
   
  -    ${python}/bin/${python.executable} setup.py install --install-lib=$out/lib/${python.libPrefix}/site-packages \
  -                                                        --prefix="$out" ${lib.concatStringsSep " " setupPyInstallFlags}
  +    ${python}/bin/${python.executable} setup.py install \
  +      # sometimes packages specify where files should be installed outside the usual
  +      # python lib prefix, we override that back so all infrastructure (setup hooks)
  +      # work as expected
  +      --install-lib=$out/lib/${python.libPrefix}/site-packages \
  +      # instruct setuptools not to use eggs but fallback to plan package install
  +      # this also reduces one .pth file in the chain, but the main reason is to
  +      # force install process to install only scripts for the package we are
  +      # installing (otherwise it will install scripts also for dependencies)
  +      --old-and-unmanageable \
  +      --prefix="$out" ${lib.concatStringsSep " " setupPyInstallFlags}
   
       # A pth file might have been generated to load the package from
       # within its own site-packages, rename this package not to
  
positive.code:       wrapPythonPrograms
  
        # If a user installs a Python package, they probably also wants its
        # dependencies in the user environment (since Python modules don't
        # have something like an RPATH, so the only way to find the
        # dependencies is to have them in the PYTHONPATH variable).
        # TODO: better docs
        if test -e $out/nix-support/propagated-build-inputs; then
            ln -s $out/nix-support/propagated-build-inputs $out/nix-support/propagated-user-env-packages
        fi
  
        createBuildInputsPth build-inputs "$buildInputStrings"
        for inputsfile in propagated-build-inputs propagated-native-build-inputs; do
          if test -e $out/nix-support/$inputsfile; then
  
negative.code: 
  { name
  
  # by default prefix `name` e.g. "python3.3-${name}"
  , namePrefix ? python.libPrefix + "-"
  
  , buildInputs ? []
  
  # pass extra information to the distutils global configuration (think as global setup.cfg)
  , distutilsExtraCfg ? ""
  
  # propagate build dependencies so in case we have A -> B -> C,
  # C can import propagated packages by A
  , propagatedBuildInputs ? []
  
  # passed to "python setup.py install"
  