anchor.diff:  
     src = fetchPypi {
       inherit pname version;
  -    sha256 = "18h78s5ld1i6mz00w258hy29909nfr3ddq6ry9kq18agw468bks8";
  +    sha256 = "sha256-M5ysSLgN28i/0F2q4KOnNBRlGoWWkEwqiBz9Httl8mw=";
     };
   
     XDG_RUNTIME_DIR = "/tmp";
  
positive.code: in
  
  buildPythonPackage rec {
    version = "3.5.2";
    pname = "matplotlib";
    format = "setuptools";
  
  
negative.code:       echo "[libs]
        system_freetype=true
        system_qhull=true" > mplsetup.cfg
  
        substituteInPlace setup.py \
          --replace "setuptools_scm>=4,<7" "setuptools_scm>=4"
      '';
  
    # Matplotlib needs to be built against a specific version of freetype in
  