Referenced table not found in standalone Python script

Question

I'm trying to run a Python script from OSGeo4W Shell. Im doing this by typing "python-qgis C:\path\test.py"

Everything seems to go fine until the script launches the processing module. After that console gives me a lot of invalid escape sequence warnings.

Then when the script hits the SQL- algorithm it fails to find the referenced table. It still manages to load it.

ERROR: Referenced table file in query not found

Here is my script:

import sys

from qgis.core import (
QgsApplication, 
QgsProcessingFeedback, 
QgsVectorLayer,
QgsCoordinateReferenceSystem,
QgsProcessingParameterFeatureSource,
QgsProcessingFeedback
)

QGIS = 'C:\\Program Files\\QGIS 3.6\\apps\\qgis'


# Prefix
QgsApplication.setPrefixPath(('QGIS'),True)
qgs = QgsApplication([], False)
qgs.initQgis()

# Processing path
sys.path.append('C:\\Program Files\\QGIS 3.6\\apps\\qgis\\python\\')
sys.path.append('C:\\Program Files\\QGIS 3.6\\apps\\qgis\\python\\plugins')

path = 'O:\\Desktop\\Qgis\\File\\file.shp'

IN = QgsVectorLayer(path,'file','ogr')

if IN.isValid():
    print ('Success!')
else:
    print ('Failed!')

OUT = 'O:\\Desktop\\Area\\Leik\\A_Area.shp'

from qgis.analysis import QgsNativeAlgorithms
import processing
from processing.core.Processing import Processing
Processing.initialize()
QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())

AO = {
            'INPUT_DATASOURCES': IN,
            'INPUT_GEOMETRY_CRS': QgsCoordinateReferenceSystem('EPSG:3883'),
            'INPUT_GEOMETRY_FIELD': '',
            'INPUT_GEOMETRY_TYPE': None,
            'INPUT_QUERY': 'SELECT \"file\".* \nFROM \"file\"\nWHERE \"file\".\"type\" like \"a%\"',
            'INPUT_UID_FIELD': '',
            'OUTPUT': OUT,
        }

feedback = QgsProcessingFeedback()

result = processing.run('qgis:executesql', AO,feedback=feedback)

print(result)

sys.exit()

Answer 1

Those warnings about invalid escape sequences are in \lib\site-packages\requests\status_codes.py and \lib\site-packages\_plotly_utils\basevalidators.py scripts and have nothing to do with your script. Upgrade QGIS to the latest stable (3.10) or LTR (3.4) release.

When running your code I didn't find invalid escape sequence warnings. The only strange path is that one ending with '...\\python\\'.
Also, you can declare raw strings (r'...') and don't escape the special characters.

All I found was an error in the AO dictionary:
In the query, the table must be named input1 (altought the name of the input layer is file).

This code run without errors here (I have changed the path to my files and proposed other way to declare the query):

import sys

from qgis.core import (
QgsApplication, 
QgsProcessingFeedback, 
QgsVectorLayer,
QgsCoordinateReferenceSystem,
QgsProcessingParameterFeatureSource,
QgsProcessingFeedback
)

QGIS = r'C:\Program Files\QGIS 3.6\apps\qgis'


# Prefix
QgsApplication.setPrefixPath(('QGIS'),True)
qgs = QgsApplication([], False)
qgs.initQgis()

# Processing path
sys.path.append(r'C:\Program Files\QGIS 3.6\apps\qgis\python')
sys.path.append(r'C:\Program Files\QGIS 3.6\apps\qgis\python\plugins')

path = r'C:\GA\GIS\test\file.shp'

IN = QgsVectorLayer(path,'file','ogr')

if IN.isValid():
    print ('Success!')
else:
    print ('Failed!')

OUT = r'C:\GA\GIS\test\A_Area.shp'

from qgis.analysis import QgsNativeAlgorithms
import processing
from processing.core.Processing import Processing
Processing.initialize()
QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())


# Declare a query ready to be modified or include {variables}
import inspect
query = inspect.cleandoc(f'''
    SELECT "input1".*
    FROM "input1"
    WHERE "input1"."type" LIKE "a%";'''
)
print(query)


AO = {
            'INPUT_DATASOURCES': IN,
            'INPUT_GEOMETRY_CRS': QgsCoordinateReferenceSystem('EPSG:3883'),
            'INPUT_GEOMETRY_FIELD': '',
            'INPUT_GEOMETRY_TYPE': None,
            'INPUT_QUERY': query,
            'INPUT_UID_FIELD': '',
            'OUTPUT': OUT,
        }

feedback = QgsProcessingFeedback()

result = processing.run('qgis:executesql', AO,feedback=feedback)

print(result)

sys.exit()