No Output When Using Python Console In QGIS

Question

I am fairly new to using the python console in QGIS so I am not entirely sure if there is an issue with a line of code I am using or human error.

I am using this code to cycle through a point layer of 3000 points situated over around 14 vector layers that I have created. The aim of the code is to efficiently show what layers each point resides on. As each vector layer is assigned a rank I cannot do a select by location as that would take months.

When running a test of around 10 points, the code runs with no issues, but when I go to open the text file I have created for the output, it is empty.

However, interestingly when I ran the code with both the test data points and with the original dataset of 3000 still active in QGIS, an output was produced. So I am assuming the code works and produces an output when a point overlays another point but not when a point overlays a vector layer. Is this an mistake within the code or might it be another factor? For example, the text file has to be formatted in a certain way? The code is displayed below.

counter = 0

# Set the path for the output file
output_file = open(r'/Users/admin/Desktop/TestFlood.txt', 'wb')
iter_layer = QgsProject.instance().mapLayersByName('test_flood')
layers = QgsProject.instance().mapLayers().values()
for point in iter_layer[0].getFeatures():
   counter += 1
   print(counter)
   for layer in layers:
       if layer.name() != iter_layer[0].name():
           for feature in layer.getFeatures():
               if (feature.geometry().contains(point.geometry())):
                       msgout = '%s, %s \n' % (point["pcds"], layer.name())
                       unicode_message = msgout.encode('utf-8')
                       output_file.write(unicode_message)
print('Finished')
output_file.close()

I am using QGIS 3.4.9-Madeira and my OS is MacOS 10.14.6 Mojave.

Answer 1

It looks like your issue lies in the way you've tried to format your output and write it to your file.

First, instead of opening the file in binary writing ('wb') mode, try standard writing mode ('w'). Once you've done that, there's no need to encode your output string - just use output_file.write(msgout).

Note that this doesn't explicitly specify an encoding format. If that's important for you, you can specify encoding='utf-8' in the open() call.

Additionally, make sure that the only layers present in the project are the other vector layers that you want to search in. Anything else, especially a raster layer like OpenStreetMap, will cause an error when your getFeatures() call is made.

Hope this helps! If not, as always, feel free to comment below.

Answer 2

In response to comments on my previous answer, I've created a test dataset (available at https://www.dropbox.com/sh/wf2xdw2gzgci0yo/AACD2809I876ijEdpy_zjUgMa?dl=0) to make sure everything works as expected. Typing the code from the question line-by-line using the Python Console (Ctrl+Alt+P on Windows), and with normal file writing as in my previous answer, works for me. At the moment, it's unclear why the OP's problem occurred in the first place.