列表返回错误“类型为'float'的对象没有len（）”

My list is returning the error "object of type 'float' has no len()". The problem is that before asking for the list length I check if the list is in fact a list and it is. Here it is the portion of code where this error occurs

   if isinstance(sprints, list):
      if len(sprints) == 0:
         plt.xticks(firstelement)
      else:
         plt.xticks(sprints)
   else:
      print("Not a List")

仅当列表为空时才会发生此错误，当列表中有对象时可以正常工作。 我已经尝试过“如果不是冲刺” sintax，并且会发生相同的错误。 有什么建议么？