Algorithm not found by PyQGIS?

Question

I have troubles using PyQgis processing module with QGIS 3.8. For example, I can reproject a layer with QGIS graphic interface, but when using PyQgis processing module through the following script :

 import sys
 from qgis.core import *
 QgsApplication.setPrefixPath("/usr", True)
 qgs = QgsApplication([], True)
 qgs.initQgis()
 print(QgsApplication.showSettings())
 ##Processing initialization
 sys.path.extend(['/usr/share/qgis/python/plugins', '/usr/share/qgis/python/plugins/processing', 
 '/usr/share/qgis/python', '/usr/lib/qgis/plugins']) # Folder for Processing
 import processing
 from processing.core.Processing import Processing
 Processing.initialize() # needed to be able to use the functions afterwards
 ##Get and load the project instance
 project = QgsProject.instance()
 project.setCrs(QgsCoordinateReferenceSystem(2154))
 ## Chargement d'une couche
 vlayer = QgsVectorLayer('/my/place/to/save/zone_etude.shp','zone_etude','ogr')
 project.addMapLayer(vlayer)
 param = {'INPUT':'/my/place/to/save/zone_etude.shp',
 'TARGET_CRS':QgsCoordinateReferenceSystem('EPSG:4326'),
 'OUTPUT':'TEMPORARY_OUTPUT'}
 processing.run("native:reprojectlayer", param)
 project.write('/my/place/to/save/tutoproject.qgs')
 qgs.exitQgis()

This code returns :

Application state:
QGIS_PREFIX_PATH env var: 
Prefix: /usr
Plugin Path: /usr/lib/qgis/plugins
Package Data Path: /usr/share/qgis
Active Theme Name: 
Active Theme Path: /usr/share/qgis/resources/themes//icons/
Default Theme Path: :/images/themes/default/
SVG Search Paths: /usr/share/qgis/svg/
 /home/edelb/.local/share/profiles/default/svg/
User DB Path: /usr/share/qgis/resources/qgis.db
Auth DB Path: /home/edelb/.local/share/profiles/default/qgis-auth.db
Backend TkAgg is interactive backend. Turning interactive mode on.
/usr/lib/python3/dist-packages/osgeo/gdal.py:112: DeprecationWarning:
gdal.py was placed in a namespace, it is now available as osgeo.gdal
Traceback (most recent call last):
 File "/my/place/to/save/repro_bug.py", line 26, in <module>
 processing.run("native:reprojectlayer", param)
 File "/usr/share/qgis/python/plugins/processing/tools/general.py", line 106, in run
 return Processing.runAlgorithm(algOrName, parameters, onFinish, feedback, context)
 File "/usr/share/qgis/python/plugins/processing/core/Processing.py", line 125, in runAlgorithm
 raise QgsProcessingException(msg)
_core.QgsProcessingException: Error: Algorithm native:reprojectlayer not found

I am on Ubuntu 18.04, using Qgis 3.8, and I don't know how I can access several of these processing algorithms like "native:reprojectlayer" or "native:saveselectedfeatures"...
Still, some processing algorithms are reachable, as this command shows:

for alg in QgsApplication.processingRegistry().algorithms():
 print("{}:{} --> {}".format(alg.provider().name(), alg.name(), alg.displayName()))

GDAL:aspect --> Aspect
GDAL:assignprojection --> Assign projection 
... 
GRASS:r.spreadpath --> r.spreadpath 
...
QGIS:vectorlayerscatterplot --> Vector layer scatterplot
QGIS:voronoipolygons --> Voronoi polygons
QGIS:zonalstatistics --> Zonal statistics

And for example processing.algorithmHelp("qgis:voronoipolygons") returns what it is supposed to return.

• Fran Raga: you need add this line QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms()) after Processing.initialize() for use native algorithms
• Fran Raga: I add my comment as an answer then

Answer 1

To use native algorithms in a standalone application, you need to add the provider using:

QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())

It would be like this:

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