Python: How to implent Generator in a class method by this class instances

Question

in the following code

class Student(object):
   def __init__(self):
       self.vals=[9,2,4,1]

   def allstudents(self):
      self.vals.sort()
      for s in self.vals:
            yield s

jack = Student()

jack.allstudents().next() -> Of course the output is 1

jack.allstudents().next() -> Here is the problem: this line's output is still 1. Why not 2?

jack.allstudents().next() -> This line's output is still 1. Why not 4?

Could anyone give me an explanation, please?

Note that it would be conventional to implement the `__iter__` *"magic method"*, then you can just do e.g. `for s in jack:` — jonrsharpe, Aug 15 '15 at 15:11
please see [this SO QA](http://stackoverflow.com/questions/231767/what-does-the-yield-keyword-do-in-python) dedicated to `yield` — Pynchia, Aug 15 '15 at 15:40

score 3 · Answer 1 · answered Aug 15 '15 at 14:57

3

Because you are constantly calling the allstudents() method again and again. Try storing it in a variable and then calling next() on the variable assigned to it, like:

var = jack.allstudents()
var.next()
var.next()

and so on.

answered Aug 15 '15 at 14:57

Nhor

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Additionally, you might want to replace `for s in self.vals:yield s` with `yield from self.vals` for performance. – Berserker Aug 15 '15 at 15:19
thx guy! I got it~ sorry for replying late, since I have been out recently! – jxpisces Aug 28 '15 at 12:53

Python: How to implent Generator in a class method by this class instances

1 Answers1