PyQgis getting attribute values from specific features without StopIteration exception

Question

I have been trying to access the values of the attributes of certain features in a vector layer. I have tried to to as they suggest in How to read the attribute values using PyQGIS? and Getting feature attribute description with pyqgis?, but whenever i try to define the feature with next(), i get StopIteration exception. This stops my program as if it was an error. I have been working on it for quite some time, but I haven't been able to find a way around it.

Is there a way to get attribute values from specific features of the vector layer without getting stoped by "StopIteration"?

I am working in QGIS 2.18

EDIT, Code snippit:

for i in range(0, len(vaiable)):
    request = QgsFeatureRequest().setFilterFid(i)
    iterator = layer.getFeatures(QgsFeatureRequest().setFilterFid(i))
    feature = next(iterator)
    #feature = layer.getFeatures(request).next()

I have tried with both iterator and request, with but StopIterator is raised when trying to assign "feature" in both cases

Hi Kasper, can you add the code you are using for this? – Matthias Kuhn Oct 17 '18 at 14:07 — Matthias Kuhn, Oct 17 '18 at 14:07
Of course, done so in edit – Kasper Skjeggestad Oct 18 '18 at 08:30 — Kasper Skjeggestad, Oct 18 '18 at 08:30

Matthias Kuhn · Accepted Answer · 2018-10-18T10:29:27.837

1

It's quite hard to know, what exactly you have in vaiable. I assume it's an array, and given the array is [1,2,3], i would iterate over 0,1,2.

Your code is based on the assumption, that there is a feature for each of these three ids (0, 1 and 2), but the StopIteration tells us that this assumption does not hold true. At some point, the code tries to get a feature on an empty iterator.

The following code will help to get more information which ID is not there. If you just want to ignore non-existent features, remove the raise.

for i in range(0, len(vaiable)):
    request = QgsFeatureRequest().setFilterFid(i)
    iterator = layer.getFeatures(QgsFeatureRequest().setFilterFid(i))
    try:
        feature = next(iterator)
    except StopIteration:
        print('No feature with id {} found in dataset').format(i)
        raise
    #feature = layer.getFeatures(request).next()

To check which ids the features on the layer have, use this code:

print(', '.join(str(f.id()) for f in layer.getFeatures()))

edited Oct 18 '18 at 10:29

answered Oct 18 '18 at 09:29

Matthias Kuhn

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The variable changes and is supposed to be an feature for each of the ids. I did try the test, and the exception is raised already at id 0. I have been trying this in qgis console with different numbers, and StopIteration is always stopping the code – Kasper Skjeggestad Oct 18 '18 at 10:23
What is the output of print(', '.join(str(f.id()) for f in layer.getFeatures()))? That will print all the ids which are available on the layer. – Matthias Kuhn Oct 18 '18 at 10:28
1

It prints out a long list of ascending numbers (6, 16, 28, 47, 55, 77, 91, 99, 129 ... ). So, the feature ids doesn't necessarily start at 0 or 1 then? I suppose that's where I went wrong. I will rethink the code with this information. Thank you for your help – Kasper Skjeggestad Oct 18 '18 at 10:43

PyQgis getting attribute values from specific features without StopIteration exception

1 Answers1