code: def get_from_requirements(self,
                                r,                      # type: Dict[Text, Text]
                                pull_image,             # type: bool
                                force_pull=False,       # type: bool
                                tmp_outdir_prefix=None  # type: Text
                               ):
          # type: (...) -> Optional[Text]
          
  
          if not bool(spawn.find_executable('singularity')):
              raise WorkflowException('singularity executable is not available')
  
          if not self.get_image(r, pull_image, force_pull):
              raise WorkflowException(u"Container image {} not "
                                      "found".format(r["dockerImageId"]))
  
          return os.path.abspath(r["dockerImageId"])
docs: Returns the filename of the Singularity image (e.g.
          hello-world-latest.img).