Attempting to understand yield as an expression

Question

I\'m playing around with generators and generator expressions and I\'m not completely sure that I understand how they work (some reference material):

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Answer 1

Indeed - the send method is meant to work with a generator object that is the result of a co-routine you have explicitly written. It is difficult to get some meaning to it in a generator expression - though it works.

-- EDIT -- I had previously written this, but it is incorrecct, as yield inside generator expressions are predictable across implementations - though not mentioned in any PEP.

generator expressions are not meant to have the yield keyword - I am not shure the behavior is even defined in this case. We could think a little and get to what is happening on your expression, to meet from where those "None"s are coming from. However, assume that as a side effect of how the yield is implemented in Python (and probably it is even implementation dependent), not as something that should be so.

The correct form for a generator expression, in a simplified manner is:

( for  in  [if ])

so, is evaluated for each value in the - not only is yield uneeded, as you should not use it.

Both yield and the send methods are meant to be used in full co-routines, something like:

def doubler():
   value = 0
   while value < 100:
       value = 2 * (yield value)

And you can use it like:

>>> a = doubler()
>>> # Next have to be called once, so the code will run up to the first "yield"
... 
>>> a.next()
0
>>> a.send(10)
20
>>> a.send(20)
40
>>> a.send(23)
46
>>> a.send(51)
Traceback (most recent call last):
  File "", line 1, in 
StopIteration
>>>