[TrianguloY]

But wait, there's more, you can send data back to the function! (Will be returned as the yield output)

https://stackoverflow.com/questions/20579756/passing-value-t...

And don't forget "yield from" (same as yielding all values in a list, but keeps the original generator! You can send data back to the list if it is itself another generator!)

[noitpmeder]

Anyone have good examples of how/when to actually use this? I've personally never interacted with or written a generator that expects to receive values.

[strunz]

I actually had a great use case for this last week. Needed to flatten a list of nested dicts, e.g.:

  [
    {"name": "/dev/loop0"},
    {"name": "/dev/loop1"},
    {"name": "/dev/loop2"},
    {
      "name": "/dev/sda",
      "children":
        [
          {
            "name": "/dev/sda1",
            "children":
              [{"name": "/dev/mapper/lubuntu--vg-root"}, {"name": "/dev/mapper/lubuntu--vg-swap_1"}],
          },
        ],
    },
    {"name": "/dev/sdb", "children": [{"name": "/dev/sdb1"}, {"name": "/dev/sdb2"}]},
    {"name": "/dev/sdc", "children": [{"name": "/dev/sdc1"}, {"name": "/dev/sdc9"}]},
  ]

Wound up writing a recursive generator (with some help from #python on IRC):

  def flatten(items):
      for item in items:
          yield {k:v for k,v in item.items() if k != 'children'}
          if 'children' in item:
              yield from flatten(item['children'])

which results in:

  [{'name': '/dev/loop0'},
   {'name': '/dev/loop1'},
   {'name': '/dev/loop2'},
   {'name': '/dev/sda'},
   {'name': '/dev/sda1'},
   {'name': '/dev/mapper/lubuntu--vg-root'},
   {'name': '/dev/mapper/lubuntu--vg-swap_1'},
   {'name': '/dev/sdb'},
   {'name': '/dev/sdb1'},
   {'name': '/dev/sdb2'},
   {'name': '/dev/sdc'},
   {'name': '/dev/sdc1'},
   {'name': '/dev/sdc9'}]

[TrianguloY]

I see your function and "yield" (pun definitely intended) the following:

    def flatten(children=[], **other):
        if other: yield other
        for child in children: yield from flatten(**child)

[strunz]

That's pretty brilliant to use `children` as the keyword name, thanks!

[noitpmeder]

Thanks for the example, but I was more looking for something that uses "generator.send(...)". I definitely agree that yielding items out of generators is extremely useful, but not so sure on examples of generators that are sent values.

[luckycharms810]

This is the basis of most older async frameworks (see: Tornado, Twisted). A while ago I put together a short talk on how to go from this feature -> a very basic version of Twisted's @inline_callback decorator.

https://github.com/ltavag/async_presentation/tree/master

[pizza]

Anything with feedback control. Updating a priority queue's weights, adaptive caching, adaptive request limiting, etc. Ironically it looks like HN itself rate limited me the first time I tried to reply lol

[noman-land]

I am a python noob and this is going to take me some time to process.

[contravariant]

Best way to think about it is that a generator can throw some questions back to the caller. It always looks a bit messy though.

    question_bank={'1+1' : '2', '2+3' : '5'}

    def Quiz():
        for question, correct_answer in question_bank.items():
            answer = yield question
            if answer == correct_answer:
                print('Correct!')
            else:
                print('Wrong.')
        yield 'Finished!'
                
    question = Quiz()
    q = next(question)
    while q != 'Finished!':
        q = question.send(input(q))