Recursive Generator Error?

[Terry Reedy]

On 10/21/2012 7:29 PM, David wrote:
> I have a tree-like data structure, the basic elements are hash tables,
> and they are grouped into lists, like [[{'a':1},[{'b':2}]]].
> And I want to flat the lists and visit hash table one by one, like {'a':1}, {'b':2}.
> But my program didn't work as I wish. When it entered the 2nd
> flat_yield, it threw a GeneratorExit. Is there anything wrong?

1. The Python version is not specified.
2. You used 2.x; in 3.3 the code does exactly what I would expect, which 
is to say, nothing. No output, no error, no traceback ;-)
3. The traceback is missing from this post.

> #- - - - - - - - - -
> def flat_yield(tbl_list):
>      for t in tbl_list:
>          if type(t) == type({}):
>              yield t
>          elif type(t) == type([]):
>              flat_yield(t)

4. Think harder about what that expression does.

> a = [[{'a':1},[{'b':2}]]]
> for i in flat_yield(a):
>      print i

Hint: it calls flat_yield, which returns a generator, which is then 
discarded. You might have well written 'pass'.

Solution: use the recursively called generator and recursively yield 
what it yields. Replace 'flat_yield(t)' with

             for item in flat_yield(t):
                 yield item

and the output is what you want.

-- 
Terry Jan Reedy