anchor.diff:    inherit (stdenv) isDarwin;
   in buildPythonPackage rec {
     pname = "pandas";
  -  version = "0.19.2";
  +  version = "0.20.1";
     name = "${pname}-${version}";
   
  -  src = fetchurl {
  -    url = "mirror://pypi/${builtins.substring 0 1 pname}/${pname}/${name}.tar.gz";
  -    sha256 = "6f0f4f598c2b16746803c8bafef7c721c57e4844da752d36240c0acf97658014";
  +  src = fetchPypi {
  +    inherit pname version;
  +    sha256 = "42707365577ef69f7c9c168ddcf045df2957595a9ee71bc13c7997eecb96b190";
     };
   
     LC_ALL = "en_US.UTF-8";
  -  buildInputs = [ nose glibcLocales ] ++ optional isDarwin libcxx;
  +  buildInputs = [ pytest glibcLocales ] ++ optional isDarwin libcxx;
     propagatedBuildInputs = [
       cython
       dateutil
  
positive.code:   '';
  
    # The flag `-A 'not network'` will disable tests that use internet.
    # The `-e` flag disables a few problematic tests.
    checkPhase = ''
      runHook preCheck
      # The flag `-w` provides the initial directory to search for tests.
      # The flag `-A 'not network'` will disable tests that use internet.
      nosetests -w $out/${python.sitePackages}/pandas --no-path-adjustment -A 'not slow and not network' \
        --verbosity=3
       runHook postCheck
    '';
  
    meta = {
  
negative.code: { buildPythonPackage
  , fetchPypi
  , python
  , stdenv
  , fetchurl
  , pytest
  , glibcLocales
  , cython
  , dateutil
  