Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #41108 > unrolled thread

del not working for (exhausted) dict iterable value (Python 3.3)

Back to article view | Back to comp.lang.python

Contents

  del not working for (exhausted) dict iterable value (Python 3.3) Nick Mellor <thebalancepro@gmail.com> - 2013-03-11 22:35 -0700
    Re: del not working for (exhausted) dict iterable value (Python 3.3) alex23 <wuwei23@gmail.com> - 2013-03-11 22:52 -0700
      Re: del not working for (exhausted) dict iterable value (Python 3.3) Nick Mellor <thebalancepro@gmail.com> - 2013-03-12 15:40 -0700
      Re: del not working for (exhausted) dict iterable value (Python 3.3) Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2013-03-13 05:02 +0100

#41108 — del not working for (exhausted) dict iterable value (Python 3.3)

Hi all,

event['Items'] is an exhausted (all used up) iterable.

Now I do the following (lines 142-4):

            event.update({'Attributes': filtered_attributes})
            del event['Items']
            yield event

and get a KeyError on the del statement. 'Items' is a key in the event dictionary at this point.

The full file is here:

https://gist.github.com/nickmellor/5140516

I can get round it by copying all but the 'Items' member to a new dictionary, but obviously I don't want to.

Is there some deep design in Python here, that it won't delete a dict value that's an (exhausted) iterator, or have I found a bug?

Thanks for any help,

Nick

[toc] | [next] | [standalone]

#41109

On Mar 12, 3:35 pm, Nick Mellor <thebalance...@gmail.com> wrote:
> event['Items'] is an exhausted (all used up) iterable.
>
> Now I do the following (lines 142-4):
>
>             event.update({'Attributes': filtered_attributes})
>             del event['Items']
>             yield event
>
> and get a KeyError on the del statement.
>
> Is there some deep design in Python here, that it won't delete a
> dict value that's an (exhausted) iterator, or have I found a bug?

You're effectively doing this:

>>> event = dict(Items=[1,2,3])
>>> for e in event['Items']:
...     del event['Items']
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
KeyError: 'Items'

You want to move your del statement up an indentation level so it
happens after the iterator is actually exhausted, and not after the
first iteration.

[toc] | [prev] | [next] | [standalone]

#41153

Thanks Alex!

Nick

[toc] | [prev] | [next] | [standalone]

#41160

Am 12.03.2013 06:52 schrieb alex23:

> You're effectively doing this:
>
>>>> event = dict(Items=[1,2,3])
>>>> for e in event['Items']:
> ...     del event['Items']
> ...
> Traceback (most recent call last):
>    File "<stdin>", line 2, in <module>
> KeyError: 'Items'
>
> You want to move your del statement up an indentation level so it
> happens after the iterator is actually exhausted, and not after the
> first iteration.

Just to be clear: Exhausting the iterator is not the problem, as I 
thought as well at the first glance.

The problem is the fact that the loop body tuns multiple times - and so 
does the del statement. A

event = dict(Items=[1,2,3])
for e in event['Items']:
     if 'Items' in event: del event['Items']

runs perfectly, as the iterable is transformed to an iterator at the 
very start of the loop.


Thomas

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.python

csiph-web