Merging a generated polygon to an existing layer using PyQGIS

Question

I make points everyday and make it into a polygon and merge it to the previous polygon I have already made

The format of the points are in yyyy-mm-dd_Points and the polygon format is yyyymmdd_progress which is stored in my folder.

My code primarily generates polygon (variable polygon) by buffer (but I'm also open to suggestions better way to generate polygon from points), then I will manually paste the directory to the variable lay1, then it will get merged.

How can I get the directory of the layer I want to merge with the polygon I just created?

So this is my code:

  from qgis import processing
from datetime import datetime, timedelta
path_file = f'C:/Users/CMCA/Downloads'
date = datetime.strftime(datetime.now() - timedelta(2), "%Y%m%d") 
lay1 = path_file +'/'+f'{date}'+'_progress'+'.gpkg'
#lay1 = 'C:/Users/CMCA/OneDrive - Boskalis/Documents/20230323_PVDprogress.gpkg'
inlayDir = iface.activeLayer()
print("Start Polygon Process...")
print("Generating polygon")
polygon = processing.runAndLoadResults("native:buffer", 
               {'INPUT':inlayDir,
               'DISTANCE':1.5,
               'SEGMENTS':2,
               'END_CAP_STYLE':0,
               'JOIN_STYLE':0,
               'MITER_LIMIT':2,
               'DISSOLVE':True,
               'OUTPUT':'TEMPORARY_OUTPUT'})
polygon = polygon['OUTPUT']
columns_to_delete_indx = polygon.attributeList()
polygon.startEditing()
polygon.dataProvider().deleteAttributes(columns_to_delete_indx)
polygon.commitChanges()
print("merging...")
merge = processing.runAndLoadResults("native:mergevectorlayers",{'LAYERS':[lay1,polygon],
                                         'CRS':QgsCoordinateReferenceSystem('USER:100000'),
                                         'OUTPUT':'TEMPORARY_OUTPUT'})

Error:

  Traceback (most recent call last):
  File "C:\PROGRA~1\QGIS32~1.0\apps\Python39\lib\code.py", line 90, in runcode
    exec(code, self.locals)
  File "<input>", line 1, in <module>
  File "<string>", line 31, in <module>
AttributeError: 'str' object has no attribute 'attributeList'

This is the whole code I've done so far but I am having trouble with the errors :

    from qgis import processing
    from datetime import datetime, timedelta
path_file = f'C:/Users/CMCA/Downloads'

date = datetime.strftime(datetime.now() - timedelta(2), &quot;%Y%m%d&quot;) # or &quot;%Y%m%d_%H%M%S&quot;
lay1 = path_file +'/'+f'{date}'+'_progress'+'.gpkg'

#lay1 = 'C:/Users/CMCA/OneDrive - Boskalis/Documents/20230327_PVDprogress.gpkg'
inlayDir = iface.activeLayer()
P3_boundary = 'D:/QGIS/General/PhaseRev3_BoundariesOutside_v2.gpkg'

clustering = processing.runAndLoadResults(&quot;native:dbscanclustering&quot;,
                                          {'INPUT':inlayDir,
                                          'MIN_SIZE':5,
                                          'EPS':2,
                                          'DBSCAN*':False,
                                          'FIELD_NAME':'CLUSTER_ID',
                                          'SIZE_FIELD_NAME':'CLUSTER_SIZE',
                                          'OUTPUT':'TEMPORARY_OUTPUT'})

concave_Hull = processing.runAndLoadResults(&quot;qgis:concavehull&quot;,
                                            {'INPUT':clustering['OUTPUT'],
                                            'ALPHA':0.01,
                                            'HOLES':True,
                                            'NO_MULTIGEOMETRY':True,
                                            'OUTPUT':'TEMPORARY_OUTPUT'})
print(&quot;Generating polygon&quot;)

buffer = processing.run(&quot;native:buffer&quot;,
              {'INPUT':concave_Hull['OUTPUT'],
               'DISTANCE':1,
               'SEGMENTS':5,
               'END_CAP_STYLE':2,
               'JOIN_STYLE':0,
               'MITER_LIMIT':2,
               'DISSOLVE':True,
               'OUTPUT':'TEMPORARY_OUTPUT'})


polygon = buffer['OUTPUT']
columns_to_delete_indx = polygon.attributeList()
polygon.startEditing()
polygon.dataProvider().deleteAttributes(columns_to_delete_indx)
polygon.commitChanges()
polygon = iface.activeLayer()

print(&quot;merging...&quot;)

merge = processing.runAndLoadResults(&quot;native:mergevectorlayers&quot;,{'LAYERS':[lay1,polygon],
                                         'CRS':QgsCoordinateReferenceSystem('USER:100000'),
                                         'OUTPUT':'TEMPORARY_OUTPUT'})




Error:
Generating polygon
merging...
Traceback (most recent call last):
  File "C:\PROGRA~1\QGIS32~1.0\apps\Python39\lib\code.py", line 90, in runcode
    exec(code, self.locals)
  File "<input>", line 1, in <module>
  File "<string>", line 53, in <module>
  File "C:\PROGRA~1/QGIS32~1.0/apps/qgis/./python/plugins\processing\tools\general.py", line 151, in runAndLoadResults
    return Processing.runAlgorithm(alg, parameters=parameters, onFinish=handleAlgorithmResults, feedback=feedback,
  File "C:\PROGRA~1/QGIS32~1.0/apps/qgis/./python/plugins\processing\core\Processing.py", line 181, in runAlgorithm
    raise QgsProcessingException(msg)
_core.QgsProcessingException: Unable to execute algorithm
Incorrect parameter value for LAYERS

I'm not clear from the current version of your question what your process is, or what specifically you are asking for help with. Can you clarify? — Tom Brennan, Mar 26 '23 at 07:23
The error you get is because dir is a reserved keyword in Python. Hence the built-in function or method part of the error. Having said that, you can't have defined your dir variable because if you had, it would have overwritten the built-in function. — Matt, Mar 26 '23 at 13:55
I edited it again .. the path_file , date is concatenated in lay1 variable. and it suppose to fine the layer with that file name . but i still get an error — charliey, Mar 26 '23 at 14:01
Does the error correspond to the new code? According to the code in your question you are no longer trying to add a built-in function or method and a string. Please include all relevant code, otherwise it is difficult to help you. You also miss the f from the beginning of your f string (the string with the curly braces {}). — Matt, Mar 26 '23 at 15:15
I edited my script, with what you have noticed, but it gave me new error. — charliey, Mar 27 '23 at 09:43
polygon['OUTPUT'] is just a string, the path to the file where the temporary output is stored. You need to use processing.run (not runAndLoadResults) - the OUTPUT from that is a QgsVectorLayer, which will allow you to use .attributeList() — Tom Brennan, Mar 27 '23 at 10:01
This thread is becoming very muddled with the error reported being changed, reframing of the question, and now two different scripts at once. There are already 2 valid answers to the problem previously stated. I would recommend rolling back your edits and opening a new question for your new problem. — Matt, Mar 29 '23 at 08:55

Kadir Şahbaz · Answer 1 · 2023-03-27T10:44:59.713

In the last version of your question, use processing.run instead of processing.runAndLoadResults. Because runAndLoadResults methods returns {'OUTPUT': 'buffer_0ae....'}. So polygon['OUTPUT'] gives you a string. That's why you're getting the error.

Instead, use processing.run. It returns {'OUTPUT': <qgis._core.QgsVectorLayer object at 0x00...>}. In this case, polygon["OUTPUT"] gives you the layer reference in memory and you don't get that error.

Please review this answer for more detailed information.

In a nutshell, use this:

polygon = processing.run("native:buffer", ... 
polygon = polygon['OUTPUT']

If you need to add the buffer layer to the project, use also:

QgsProject.instance().addMapLayer(polygon)

score 4 · Answer 2 · answered Mar 27 '23 at 09:57

4

Calling 'OUTPUT' on the result of processing.runAndLoadResults returns a Map Layer ID (a string), not a QgsMapLayer.

Add this to get a reference to the layer:

polygon = polygon['OUTPUT']
add this line
polygon = QgsProject.instance().mapLayer(polygon)
should now work
columns_to_delete_indx = polygon.attributeList()

answered Mar 27 '23 at 09:57

Matt

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I have added the whole script i made so far here, if you could please check what is wrong ? – charliey Mar 29 '23 at 05:29
I got another Error: Traceback (most recent call last): File "C:\PROGRA~1\QGIS32~1.0\apps\Python39\lib\code.py", line 90, in runcode exec(code, self.locals) File "", line 1, in File "", line 45, in TypeError: QgsProject.mapLayer(): argument 1 has unexpected type 'QgsVectorLayer' – charliey Mar 29 '23 at 09:09

Merging a generated polygon to an existing layer using PyQGIS

2 Answers2

add this line

should now work