generator object or 'send' method?

andrew cooke andrew at
Mon Feb 9 15:07:41 EST 2009

If I were experimenting with Python to see just how far I could push
coroutines at the moment, I would use .send() and look at how I could
factor things into a small library (containing, for example, your
trap-and-response secondary generator).

But if this was paid work, I would write a class with a __next__ method
and do things explicitly.

In answer to your PS, via a roundabout route: I've done something similar
recently by using .throw() to raise an exception in the body of the
generator.  This was done with a reset() function.  So, for example:

  mygen = ...
  a = next(mygen)
  b = next(mygen)
  c = next(mygen)

And in the generator:

  while True:
      yield ...
    catch ResetException:
      yield # discarded by the reset function

And finally:

  def reset(gen):

In that case, I needed an extra "yield" that did nothing.


Aaron Brady wrote:
> Hello,
> I am writing a generator to return a sequence of numbers with some
> variation.  The parameters of the variation can be changed by the
> caller, even after the generator is started.  My question is, is it
> better to wrap the generator in an object, so that the parameters can
> be changed just by an attribute access?  Or keep the generator clear,
> and modify parameters with a 'send' call?
> P.S.  It would receive the 'send' from a different point in control
> flow than its usual 'next'.  Should it repeat a value if it receives a
> 'send'?  Or should I wrap it in a secondary 'trap_send_and_repeat'
> generator?
> Thanks sincerely as always.
> --

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