How to yield results from a nested generator function?

Question

I have a function which yields results as it downloads them. For the purposes of this question, lets say I yield a sting once every second but I want a convenience function to wrap my generator:

import time  def GeneratorFunction(max_val):     for i in range(0,5):         time.sleep(1)         yield "String %d"%i  def SmallGenerator():     yield GeneratorFunction(3)  for s in SmallGenerator():     print s 

...why doesn't that just print the 5 strings I'm expecting? Instead it appears to return the generator functio:

<generator object GeneratorFunction at 0x020649B8> 

How can I get this to yield the strings as a normal generator function would?

Answer 1

You may have to use the new yield from, available since Python 3.3, known as “delegated generator”.

If I understood the question correctly, I came to the same issue, and found an answer elsewhere.

I wanted to do something like this:

def f():      def g():          do_something()         yield x         …         yield y      do_some_other_thing()     yield a     …     g()  # Was not working.     yield g()  # Was not what was expected neither; yielded None.     …     yield b 

I now use this instead:

yield from g()  # Now it works, it yields x and Y. 

I got the answer from this page: Python 3: Using "yield from" in Generators - Part 1 (simeonvisser.com).