Re: [QGIS-Developer] FeatureIterator Python question

[David Marteau]

Sorry, it has already been aswered, did not see the threads.


> Le 15 sept. 2017 à 16:46, David Marteau  a écrit :
> 
> Hi
> 
> If  FeatureIterator is a true iterator then use:
> 
> feature = next(FeatureIterator)
> 
> 
>> Le 15 sept. 2017 à 14:43, Andreas Neumann > > a écrit :
>> 
>> Hi,
>> 
>> While porting a project from QGIS 2x to 3x I came across a Python issue:
>> 
>> In QGIS 2.x I had a code like below working:
>> 
>> feature = FeatureIterator.next()
>> 
>> In QGIS 3x it says that object has no attribut next.
>> 
>> How do I access the first result of a feature iterator in QGIS 3?
>> 
>> I don't want to loop, because I know that my FeatureIterator always has just 
>> one result. I just want to access this first feature.
>> 
>> Thanks for your help,
>> 
>> Andreas
>> 
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> 

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Re: [QGIS-Developer] FeatureIterator Python question

[David Marteau]

Hi

If  FeatureIterator is a true iterator then use:

feature = next(FeatureIterator)


> Le 15 sept. 2017 à 14:43, Andreas Neumann  a écrit :
> 
> Hi,
> 
> While porting a project from QGIS 2x to 3x I came across a Python issue:
> 
> In QGIS 2.x I had a code like below working:
> 
> feature = FeatureIterator.next()
> 
> In QGIS 3x it says that object has no attribut next.
> 
> How do I access the first result of a feature iterator in QGIS 3?
> 
> I don't want to loop, because I know that my FeatureIterator always has just 
> one result. I just want to access this first feature.
> 
> Thanks for your help,
> 
> Andreas
> 
> ___
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Re: [QGIS-Developer] FeatureIterator Python question

[Andreas Neumann]

Thanks Matthias for explaining about that. Good to know.

Andreas


On 15.09.2017 16:22, Matthias Kuhn wrote:

Hi Andreas,

that will be done automatically when the iterator scopes out or the last
feature is yielded.
There is normally no reason to care about this method.

Matthias

On 09/15/2017 04:04 PM, Andreas Neumann wrote:

Just a quick followup question.

I see that the QgsFeatureIterator has a close method.

Should Python authors care about closing an existing feature iterator or
would this be automatically done when the script stops executing?

Andreas


On 15.09.2017 15:48, Andreas Neumann wrote:

Hi Matteo and Matthias,

Thanks - that works fine. I did not know that this changed in Python 3.

All the poor QGIS book authors who need to rewrite their books ...
about this Python changes.

Helps a lot!

Andreas



On 15.09.2017 15:44, matteo wrote:

Hi Andreas,

if I'm not wrong the next method is not been removed, it is a python
3 *fix*

https://stackoverflow.com/questions/1073396/is-generator-next-visible-in-python-3-0


so instead of:

it = layer.getFeatures()
it.next()

just type

it = layer.getFeatures()
next(it)

Matteo
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Re: [QGIS-Developer] FeatureIterator Python question

[Matthias Kuhn]

Hi Andreas,

that will be done automatically when the iterator scopes out or the last
feature is yielded.
There is normally no reason to care about this method.

Matthias

On 09/15/2017 04:04 PM, Andreas Neumann wrote:
> Just a quick followup question.
> 
> I see that the QgsFeatureIterator has a close method.
> 
> Should Python authors care about closing an existing feature iterator or
> would this be automatically done when the script stops executing?
> 
> Andreas
> 
> 
> On 15.09.2017 15:48, Andreas Neumann wrote:
>> Hi Matteo and Matthias,
>>
>> Thanks - that works fine. I did not know that this changed in Python 3.
>>
>> All the poor QGIS book authors who need to rewrite their books ...
>> about this Python changes.
>>
>> Helps a lot!
>>
>> Andreas
>>
>>
>>
>> On 15.09.2017 15:44, matteo wrote:
>>> Hi Andreas,
>>>
>>> if I'm not wrong the next method is not been removed, it is a python
>>> 3 *fix*
>>>
>>> https://stackoverflow.com/questions/1073396/is-generator-next-visible-in-python-3-0
>>>
>>>
>>> so instead of:
>>>
>>> it = layer.getFeatures()
>>> it.next()
>>>
>>> just type
>>>
>>> it = layer.getFeatures()
>>> next(it)
>>>
>>> Matteo
>>> ___
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Re: [QGIS-Developer] FeatureIterator Python question

[Matthias Kuhn]

I was also thinking about that.
I would just miss this method because it's used so often and the
alternative approaches just require more typing.

+1 for this

On 09/15/2017 03:53 PM, Nathan Woodrow wrote:
> I think we could just implement out own next method to avoid that break
> would be easy enough.
> 
> On Fri, Sep 15, 2017 at 11:48 PM, Andreas Neumann  > wrote:
> 
> Hi Matteo and Matthias,
> 
> Thanks - that works fine. I did not know that this changed in Python 3.
> 
> All the poor QGIS book authors who need to rewrite their books ...
> about this Python changes.
> 
> Helps a lot!
> 
> Andreas
> 
> 
> 
> 
> On 15.09.2017 15:44, matteo wrote:
> 
> Hi Andreas,
> 
> if I'm not wrong the next method is not been removed, it is a
> python 3 *fix*
> 
> 
> https://stackoverflow.com/questions/1073396/is-generator-next-visible-in-python-3-0
> 
> 
> 
> so instead of:
> 
> it = layer.getFeatures()
> it.next()
> 
> just type
> 
> it = layer.getFeatures()
> next(it)
> 
> Matteo
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> 
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> 
> 
> 
> 
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Re: [QGIS-Developer] FeatureIterator Python question

[Andreas Neumann]

Just a quick followup question.

I see that the QgsFeatureIterator has a close method.

Should Python authors care about closing an existing feature iterator or 
would this be automatically done when the script stops executing?


Andreas


On 15.09.2017 15:48, Andreas Neumann wrote:

Hi Matteo and Matthias,

Thanks - that works fine. I did not know that this changed in Python 3.

All the poor QGIS book authors who need to rewrite their books ... 
about this Python changes.


Helps a lot!

Andreas



On 15.09.2017 15:44, matteo wrote:

Hi Andreas,

if I'm not wrong the next method is not been removed, it is a python 
3 *fix*


https://stackoverflow.com/questions/1073396/is-generator-next-visible-in-python-3-0 



so instead of:

it = layer.getFeatures()
it.next()

just type

it = layer.getFeatures()
next(it)

Matteo
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Re: [QGIS-Developer] FeatureIterator Python question

[Nathan Woodrow]

I think we could just implement out own next method to avoid that break
would be easy enough.

On Fri, Sep 15, 2017 at 11:48 PM, Andreas Neumann 
wrote:

> Hi Matteo and Matthias,
>
> Thanks - that works fine. I did not know that this changed in Python 3.
>
> All the poor QGIS book authors who need to rewrite their books ... about
> this Python changes.
>
> Helps a lot!
>
> Andreas
>
>
>
>
> On 15.09.2017 15:44, matteo wrote:
>
>> Hi Andreas,
>>
>> if I'm not wrong the next method is not been removed, it is a python 3
>> *fix*
>>
>> https://stackoverflow.com/questions/1073396/is-generator-
>> next-visible-in-python-3-0
>>
>> so instead of:
>>
>> it = layer.getFeatures()
>> it.next()
>>
>> just type
>>
>> it = layer.getFeatures()
>> next(it)
>>
>> Matteo
>> ___
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>>
>
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Re: [QGIS-Developer] FeatureIterator Python question

[Andreas Neumann]

Hi Matteo and Matthias,

Thanks - that works fine. I did not know that this changed in Python 3.

All the poor QGIS book authors who need to rewrite their books ... about 
this Python changes.


Helps a lot!

Andreas



On 15.09.2017 15:44, matteo wrote:

Hi Andreas,

if I'm not wrong the next method is not been removed, it is a python 3 *fix*

https://stackoverflow.com/questions/1073396/is-generator-next-visible-in-python-3-0

so instead of:

it = layer.getFeatures()
it.next()

just type

it = layer.getFeatures()
next(it)

Matteo
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Re: [QGIS-Developer] FeatureIterator Python question

[Matthias Kuhn]

I quickly googled for the reason for this

PEP 3114 (https://www.python.org/dev/peps/pep-3114/)

So next() was renamed to __next__() for consistency, because it's a
builtin method.

iterator.__next__() or next(iterator) should yield the same item.

Matthias

On 09/15/2017 03:44 PM, matteo wrote:
> Hi Andreas,
> 
> if I'm not wrong the next method is not been removed, it is a python 3 *fix*
> 
> https://stackoverflow.com/questions/1073396/is-generator-next-visible-in-python-3-0
> 
> so instead of:
> 
> it = layer.getFeatures()
> it.next()
> 
> just type
> 
> it = layer.getFeatures()
> next(it)
> 
> Matteo
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Re: [QGIS-Developer] FeatureIterator Python question

[matteo]

Hi Andreas,

if I'm not wrong the next method is not been removed, it is a python 3 *fix*

https://stackoverflow.com/questions/1073396/is-generator-next-visible-in-python-3-0

so instead of:

it = layer.getFeatures()
it.next()

just type

it = layer.getFeatures()
next(it)

Matteo
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Re: [QGIS-Developer] FeatureIterator Python question

[Matthias Kuhn]

Hi Andreas,

that hasn't been a QGIS decision but a python3 one.

next(featureIterator) is the way proposed for python3. I am not sure
about the reasons for this change though.

Matthias

On 09/15/2017 03:40 PM, Andreas Neumann wrote:
> Hi,
> 
> Found out that I can access my first feature like:
> 
> feature = list(FeatureIterator)[0]
> 
> but not sure if this is recommended and efficient.
> 
> Why was the next() method of the feature iterator removed in QGIS 3? Is
> there a particular reason for that?
> 
> Thanks,
> 
> Andreas
> 
> 
> On 15.09.2017 14:43, Andreas Neumann wrote:
>> Hi,
>>
>> While porting a project from QGIS 2x to 3x I came across a Python issue:
>>
>> In QGIS 2.x I had a code like below working:
>>
>> feature = FeatureIterator.next()
>>
>> In QGIS 3x it says that object has no attribut next.
>>
>> How do I access the first result of a feature iterator in QGIS 3?
>>
>> I don't want to loop, because I know that my FeatureIterator always
>> has just one result. I just want to access this first feature.
>>
>> Thanks for your help,
>>
>> Andreas
>>
>> ___
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>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> 
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[QGIS-Developer] FeatureIterator Python question

[Andreas Neumann]

Hi,

While porting a project from QGIS 2x to 3x I came across a Python issue:

In QGIS 2.x I had a code like below working:

feature = FeatureIterator.next()

In QGIS 3x it says that object has no attribut next.

How do I access the first result of a feature iterator in QGIS 3?

I don't want to loop, because I know that my FeatureIterator always has 
just one result. I just want to access this first feature.


Thanks for your help,

Andreas

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