code: def which(cls, cmd):
          
          abs_path_cmd = None
          if sys.version_info >= (3, 3):
              abs_path_cmd = shutil.which(cmd)
          else:
              abs_path_cmd = find_executable(cmd)
          return abs_path_cmd
docs: Return an absolute path of the command.
  
          It behaves like "which command".