code: def _get_python_cmd(self):
          
          file_names = ["pypy.exe", "python.exe", "python"]
          executable = sys.executable
          if executable is not None:
              executable = os.path.split(executable)[1]
              file_names.insert(0, executable)
  
          return self._get_bin_file(*file_names)
docs: return the python executable in the virtualenv.
          Try first sys.executable but use fallbacks.