docs: def load_requirements(self):
          """If there are python library requirements set, append the python dir
          to the path."""
  
          for module_name, pip_name in iteritems(self.metadata.requirements):
              extant = self.dataset.config.requirements[module_name].url
  
              force = (extant and extant != pip_name)
  
              self._library.install_packages(module_name, pip_name, force=force)
  
              self.dataset.config.requirements[module_name].url = pip_name
  
          python_dir = self._library.filesystem.python()
          sys.path.append(python_dir)