Re: yield in try/finally case

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From	Peter Otten <__peter__@web.de>
Newsgroups	comp.lang.python
Subject	Re: yield in try/finally case
Date	Thu, 03 Mar 2016 17:20:02 +0100
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Random832 wrote:

> On Thu, Mar 3, 2016, at 08:47, Peter Otten wrote:
>> This is because the last generator uf = upperfile(...) is not garbage-
>> collected and wasn't explicitly closed either.
> 
> But the program hasn't ended yet when you run your assertion.

If your expectations are in line with Python's actual behaviour -- then 
fine. Normally someone who writes

with acquire_resource() as r:
    use(r)
assert r was released

wants the resource to be released when the with suite is left.

When the with-statement is moved into a generator

def gen_resource():
    with acquire_resource() as r:
        yield r

for r in gen_resource():
    use(r)
    break # use(r) triggering an exception would have the same effect
assert r was released # may fail

you are at the mercy of the Python interpreter's garbage collection 
strategy. 

Of course you are exiting the for-suite, not the with-suite. Nevertheless 
this surprised me when Oscar pointed it out the first time.

Thread

yield in try/finally case 刘琦帆 <lqf.txx@gmail.com> - 2016-03-03 03:52 -0800
  Re: yield in try/finally case Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-03-03 12:13 +0000
    Re: yield in try/finally case 刘琦帆 <lqf.txx@gmail.com> - 2016-03-03 04:52 -0800
      Re: yield in try/finally case Peter Otten <__peter__@web.de> - 2016-03-03 14:47 +0100
      Re: yield in try/finally case Random832 <random832@fastmail.com> - 2016-03-03 10:12 -0500
      Re: yield in try/finally case Peter Otten <__peter__@web.de> - 2016-03-03 17:20 +0100
      Re: yield in try/finally case Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-03-03 16:24 +0000
  Re: yield in try/finally case Random832 <random832@fastmail.com> - 2016-03-03 10:00 -0500
    Re: yield in try/finally case Steven D'Aprano <steve@pearwood.info> - 2016-03-04 02:57 +1100

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