[Python-ideas] Anonymous blocks (again):

[Lakshmi Vyas]

> Perhaps a concrete (even if toy or made-up) example might help me
> understand.

Not sure if this example fits Juancarlo's criterion:

Here is a place where I really craved for blocks and resorted to using a 
context manager + decorators:

https://github.com/gitbot/gitbot/blob/master/gitbot/lib/s3.py#L140-L169

The use case is essentially: recursively loop through a folder and push 
to Amazon S3 evaluating
rules for each file / folder.


Here is the implementation:
https://github.com/lakshmivyas/fswrap/blob/master/fswrap.py#L317-L439


Just removing the need for the decorators would make this pattern
completely acceptable *for me*.


Thanks
Lakshmi


Steven D'Aprano wrote:
> On Mon, May 13, 2013 at 03:17:15PM +1000, Nick Coghlan wrote:
>> On Mon, May 13, 2013 at 2:47 PM, Steven D'Aprano<steve at pearwood.info>  wrote:
>>> On 13/05/13 13:58, Juancarlo Añez wrote:
>>>
>>>> I don't want new syntax (I think I don't).
>>>>
>>>> What I want is to be able to invoke a block of code repeatedly, within a
>>>> context, and in a pythonic way.
>>> Surely that would be:
>>>
>>> with context():
>>>      while condition: # or a for loop
>>>          block of code goes here
>>>
>>>
>>> If you want something different to this, then I think you do want new
>>> syntax. Otherwise, what do you gain beyond what can already be done now?
>>>
>>> Or am I missing something?
>> Ruby uses anonymous callbacks for things where Python instead uses
>> dedicated syntax:
>>
>> Python ->  Ruby
>>
>> decorated function definitions ->  callbacks
>> for loops + iterator protocol ->  callbacks
>> with statements + context management protocol ->  callbacks
>> callbacks ->  callbacks (but with much nicer syntax)
>>
>> Blocks are a *really* nice way of doing callbacks, so nice that Ruby
>> just doesn't have some of the concepts Python does - it uses callbacks
>> instead.
>
> I'm obviously still missing something, because I'm aware of Ruby's
> blocks, but I don't quite see how they apply to Juancarlo's *specific*
> use-case, as described above.
>
> Unless Juancarlo's use-case is more general than I understood, it seems
> to me that we don't need blocks, anonymous or otherwise, to "invoke a
> block of code repeatedly, within a context", in a Pythonic way.
>
> Perhaps a concrete (even if toy or made-up) example might help me
> understand. The only thing I can think of is, if I had a bunch of
> similar loops inside the same context, where only the body of the loop
> was different, I might want to factor it out something like this:
>
>
> the_block = {define a block of code, somehow}
>
> def do_stuff(block):
>      with context:
>          while condition:
>              {execute the block of code}
>
>
> do_stuff(the_block)
> do_stuff(another_block)
>
>
> but I think that requires new syntax, and Juancarlo specifically says he
> doesn't want new syntax.
>
>
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