Implementation of __exit__ interface

[leighton]

I would like to use plyvel in a notebook development environment (ipython). Supporting a graceful close (i.e. lock release) between code evaluations using the __exit__ interface would be great for dynamic evaluation environments. I would make a pull request but I think this change is trivial and you'd have it done before breakfast :)

[wbolster]

hmm. i'm not sure what you want to achieve. note that iterators and write batches already implement the context manager protocol, meaning they can be used in a with block.

do you mean that you want to allow a DB instance to be used as a context manager? i don't see any use case for that...

additionally, i don't code before breakfast. ;)

[leighton]

with plyvel.DB('./_db') as db:
  print db.get('key')

__exit__ will close the "connection" and release the lock in the level db directory

Use case: long running processes that infrequently access the database where one wishes to close the connection to avoid contention.

[wbolster]

the contextlib module from the stdlib has a closing() context manager helper which might help here:

from contextlib import closing

with closing(plyvel.DB('./_db') as db:
  print db.get('key')

alternatively you could write a context manager wrapper if you want more flexibility and less repetition in your code (e.g. no repeated db names). easiest way is to use contextlib again:

from contextlib import contextmanager

@contextmanager
def magic_db():
    db = plyvel.DB('./_db')
    try:
        yield db
    finally:
        db.close()

...which can be used like this:

with magic_db() as db:
    db.get(b'foo')

[tlevine]

Since we're talking about coding patterns: I often code before breakfast, but I rarely connect to the internet before breakfast.

[geyang]

good pattern.