What's a provider in PyQGIS and how many types of providers exist?

Question

What's a provider in PyQGIS and how many types of providers exist?
I am really not sure what a provider does. There is an example below from PyQGIS cookbook where a provider is used to load a QgsVectorLayer.
#get the path to the shapefile e.g. /home/project/data/ports.shp
path_to_airports_layer = "testdata/airports.shp"

#The format is:
vlayer = QgsVectorLayer(data_source, layer_name, provider_name)

vlayer = QgsVectorLayer(path_to_airports_layer, "Airports layer", "ogr")

user30184 · Accepted Answer

Provider is a piece of code that reads and perhaps writes data from some source. The official providers you can find from the source code but there are also other providers that users have written for their special needs. Check these two directories:
https://github.com/qgis/QGIS/tree/master/src/core/providers

arcgis
ept
gdal
memory
meshmemory
ogr

https://github.com/qgis/QGIS/tree/master/src/providers

arcgisrest
db2
delimitedtext
geonode
gpx
grass
mdal
mssql
oracle
ows
pdal
postgres
spatialite
virtual
wcs
wfs
wms

GDAL and OGR providers can read any format that GDAL supports, that is https://gdal.org/drivers/raster/index.html and https://gdal.org/drivers/vector/index.html. It is possible to read some formats either with a native provider or by using GDAL/OGR (for example SpatiaLite).

Kadir Şahbaz · Answer

You can use QgsProviderRegistry.instance().providerList() to get the whole list of all available data provider keys.
# OUTPUT
['DB2', 'OAPIF', 'WFS', 'arcgisfeatureserver', 'arcgismapserver',
 'delimitedtext', 'gdal', 'geonode', 'gpx', 'grass', 'grassraster',
 'mdal', 'memory', 'mesh_memory', 'mssql', 'ogr', 'ows', 'postgres', 
 'postgresraster', 'spatialite', 'vectortile', 'virtual', 'wcs', 'wms']

What's a provider in PyQGIS and how many types of providers exist?

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