code: def item_from_topics(key, topics):
      
  
      if re.match("{\d+}", key):
          pos = int(key.strip("{}"))
          try:
              binding = topics[pos]
          except IndexError:
              raise IndexError(pos + 1)
  
      else:
          echo("be.yaml template key not recognised")
          sys.exit(PROJECT_ERROR)
  
      return binding
docs: Get binding from `topics` via `key`
  
      Example:
          {0} == hello --> be in hello world
          {1} == world --> be in hello world
  
      Returns:
          Single topic matching the key
  
      Raises:
          IndexError (int): With number of required
              arguments for the key