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[Python-Dev] PEP 525, third round, better finalization

Yury Selivanov yselivanov.ml at gmail.com
Sat Sep 3 15:16:30 EDT 2016 
Hi Oscar,
> I don't think PyPy is in breach of the language spec here. Python made
> a decision a long time ago to shun RAII-style implicit cleanup in
> favour if with-style explicit cleanup.
>
> The solution to this problem is to move resource management outside of
> the generator functions. This is true for ordinary generators without
> an event-loop etc. The example in the PEP is
>
> async def square_series(con, to):
>      async with con.transaction():
>          cursor = con.cursor(
>              'SELECT generate_series(0, $1) AS i', to)
>          async for row in cursor:
>              yield row['i'] ** 2
>
> async for i in square_series(con, 1000):
>      if i == 100:
>          break
>
> The normal generator equivalent of this is:
>
> def square_series(con, to):
>      with con.transaction():
>          cursor = con.cursor(
>              'SELECT generate_series(0, $1) AS i', to)
>          for row in cursor:
>              yield row['i'] ** 2
>
> This code is already broken: move the with statement outside to the
> caller of the generator function.

Exactly.

I used 'async with' in the PEP to demonstrate that the cleanup 
mechanisms are powerful enough to handle bad code patterns.

Thank you,
Yury
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