python build-in method next act strange : [enter image description here][1]


  [1]: https://i.stack.imgur.com/0YdGV.png

When I use a imported package, I use an object that it give to me. I found it have next method so I just try use next() build-in function to generate next item of it,but something is wrong. And i wonder what is the built-in method of an Object, I never see it before. And i am using python 2.7.12
Thank you!