python3Packages.paddlepaddle: fix evaluation error when selecting unsupported...

  version = sources.version;

  format = "wheel";

  pyShortVersion = "cp${builtins.replaceStrings [ "." ] [ "" ] python.pythonVersion}";

  hash =

    if cudaSupport then

      sources."${stdenv.hostPlatform.system}"."gpu"."cu${

        lib.replaceStrings [ "." ] [ "" ] cudaPackages.cudatoolkit.version

      }"."${pyShortVersion}"

    else

      sources."${stdenv.hostPlatform.system}"."cpu"."${pyShortVersion}"

        or (throw "Unsupported system: ${stdenv.hostPlatform.system}");

  platform = sources."${stdenv.hostPlatform.system}".platform;

  cudaVersion = "cu${lib.replaceStrings [ "." ] [ "" ] cudaPackages.cudatoolkit.version}";

  throwSystem = throw "Unsupported system: ${stdenv.hostPlatform.system}";

  systemSources = sources."${stdenv.hostPlatform.system}" or throwSystem;

  supportedCudaVersions = lib.concatStringsSep ", " (builtins.attrNames systemSources.gpu);

  throwCuda = throw "Unsupported CUDA version: ${cudaVersion}. Supported versions: ${supportedCudaVersions}";

  platformSources =

    if cudaSupport then systemSources.gpu.${cudaVersion} or throwCuda else systemSources.cpu;

  throwPython = throw "Unsupported python version: ${pyShortVersion}";

  hash = platformSources.${pyShortVersion} or throwPython;

  platform = sources.${stdenv.hostPlatform.system}.platform;

  src =

    if cudaSupport then

      (fetchurl {

        url = "https://paddle-whl.bj.bcebos.com/stable/cu${

          lib.replaceStrings [ "." ] [ "" ] cudaPackages.cudatoolkit.version

        }/paddlepaddle-gpu/paddlepaddle_gpu-${version}-${pyShortVersion}-${pyShortVersion}-linux_x86_64.whl";

        url = "https://paddle-whl.bj.bcebos.com/stable/${cudaVersion}/paddlepaddle-gpu/paddlepaddle_gpu-${version}-${pyShortVersion}-${pyShortVersion}-linux_x86_64.whl";

        inherit hash;

      })

    else