[IronPython] try...finally in yield

[Curt Hagenlocher]

Maybe I don't understand the problem you're having.  Can you describe it
with a little more detail?  When exactly do you want the file to be closed?

2009/3/29 Adam Brand <adamb at silverkeytech.com>

>  We are using 2.0 beta I think as part of ipy for asp.net. I don’t think
> close() is implemented in that version… Am I wrong?
>
>
>
> Harry (who made it) suggested this:
>
> def _process(xr):
>   while xr.Read():
>     xr.MoveToContent()
>     node = XmlNode(xr)
>     yield node
>     if xr.IsEmptyElement:
>       node = XmlNode(xr, endElement=True)
>       yield node
>
>
>
> def load(xml):
>   """generates an iterator over the XmlNodes in the stream of XML
> represented by the xml argument"""
>   if isinstance(xml, XmlReader):
>     for n in _process(xml): yield n
>   else:
>     with XmlReader.Create(xml) as xr:
>       for n in _process(xr): yield n
>
>
>
>
>
> Adam Brand
>
> SilverKey Technologies
>
>
>
> *From:* users-bounces at lists.ironpython.com [mailto:
> users-bounces at lists.ironpython.com] *On Behalf Of *Curt Hagenlocher
> *Sent:* Saturday, March 28, 2009 7:39 PM
> *To:* Discussion of IronPython
> *Subject:* Re: [IronPython] try...finally in yield
>
>
>
> So I assume you're calling close() on the generator?  A try/finally around
> the code in the generator can be used to catch the StopIteration exception
> and force the dispose.  But even better, you could say "from __future__
> import with_statement" at the top of your file and then say something like
> this:
>
> def parse(xml):
>     with XmlReader.Create(xml) as xr
>         while xr.Read():
>             [...]
>
> We automatically do the right thing when using "with" and IDisposable, so
> "with" effectively becomes like a C# "using" block.
>
> 2009/3/28 Adam Brand <adamb at silverkeytech.com>
>
> I'm using IronPython for ASP.Net...have some code (not mine,
> http://devhawk.net/2008/05/07/Deserializing+XML+With+IronPython.aspx -
> Harry Pierson's) that converts an xml file into an object. It has the below
> function:
>
> def parse(xml):
>     xr = XmlReader.Create(xml)
>     while xr.Read():
>         xr.MoveToContent()
>         node = XmlNode(xr)
>         yield node
>         if (xr.IsEmptyElement):
>             node.nodeType = XmlNodeType.EndElement
>             del node.attributes
>             yield node
>
> This code is problematic as it locks the xml file it is reading. I tried a
> try...finally to do a .Close() and .Dispose(), but the compiler was not
> happy with that. Just putting .Close() and .Dispose() at the end doesn't
> work.
>
> In reading up, I found this:
> http://docs.python.org/whatsnew/2.5.html#pep-342
>
> "The addition of the close() method has one side effect that isn’t obvious.
> close() is called when a generator is garbage-collected, so this means the
> generator’s code gets one last chance to run before the generator is
> destroyed. This last chance means that try...finally statements in
> generators can now be guaranteed to work; the finally clause will now always
> get a chance to run. The syntactic restriction that you couldn’t mix yield
> statements with a try...finally suite has therefore been removed. "
>
> I'm guessing that this isn't implemented in the version of IronPython in IP
> for ASP.Net.
>
> Does anyone have any ideas on a workaround for the generator for this
> version?
>
> Thanks,
> Adam
>
> --
> Adam Brand
>
>
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