Python - is there any way to organize a group of yields in sub function to yield outside the main function?

Question

I have a newbie question for python gurus.

I have function A that hold a lot of repeated yield-actions like so:

yield a
yield b
yield c

so it looks like:

def funA():
    …
   yield a
   yield b
   yield c
    …
   yield a
   yield b
   yield c
    …
   yield a
   yield b
   yield c

Is there any way to put all repeated yields in function and do something like that?:

def funA():
    …
   yield funB()
    …
   yield funB()
    …
   yield funB()

Update

yield a
yield b
yield c

It's just an example but in a real application its more complex sequence of yields that repeat more then once in main generator (so it's not question about organizing yields) but about sub-generators. So I'd like to avoid code duplication.

Why are you doing this? That sounds pretty terrible. You really shouldn't have more than 1 yield in a single function. Otherwise you're kind of defeating the point. — Falmarri, Nov 22 '13 at 21:56
While it is possible to do this, it sounds like what you really need is a `yield` in a loop. — user2357112, Nov 22 '13 at 21:57
@Falmarri can you share any information about why more then 1 yield in a single function is the bad practice? — Eugene Krevenets, Nov 22 '13 at 22:03
@EugeneKrevenets: It's not that more than 1 yield is in and of itself bad practice. It just indicates that your overall design is flawed. — Falmarri, Nov 22 '13 at 22:08
@Falmarri Why? Can you give more details? Or share links to articles or books about this problem? — Eugene Krevenets, Nov 22 '13 at 22:27

salezica · Accepted Answer · 2022-10-11T15:30:34.630

28

If you're using the latest and greatest python (>= 3.3), there's the yield from construct.

yield from funB()

It does exactly what you want: you can invoke a function as a sub-generator, and yield back everything it yields to you.

If you're using an earlier version of python, then I'm afraid you'll have to do it manually:

for x in funB(): yield x

If you have a dynamic set of sub-generators, you can do this:

funs = [funA, funB, funC]

for fun in funs:
    for item in fun():
        yield item

edited Oct 11 '22 at 15:30

answered Nov 22 '13 at 21:57

salezica

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Yes! Thanks! It is exactly what I need, sadly I use 2.7 version. – Eugene Krevenets Nov 22 '13 at 22:02
So Is it possible to make such a conclusion: if we have python < 3.3. It's better not to do any sub-generators and just repeat yields? So left function as it was before – Eugene Krevenets Nov 22 '13 at 22:35
On the contrary, I think your idea was good. An endless stream of `yield` statements is hard on the eyes. See my edit above for a possible grouping technique – salezica Nov 22 '13 at 22:41

score 3 · Answer 2 · answered May 11 '14 at 07:42

itertools.chain is the function you're looking for

import itertools

def funA():
    for x in range(10):
        yield x

def funB():
    for x in range(10,20):
        yield x

def funC():
    for x in range(20,30):
        yield x

def funs():
    for x in itertools.chain(funA(), funB(), funC()):
        yield x

print [x for x in funs()]

Outputs:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29]

Python - is there any way to organize a group of yields in sub function to yield outside the main function?

Update

2 Answers2