ogr2ogr --config GDAL_DATA "C:OSGeo4W64sharegdal" -f "ESRI Shapefile" C:kmfeltshapeutm322017%%a_p.shp PG:"host=%Server_host% user=%Schema_user% dbname=%Database% password=sl_nab" -sql "SELECT * FROM kmfelt_o2_p where flatenr=%%a AND komid < 1800" -t_srs EPSG:%SRID% -geomfield geo

call python %prog%5_deletefields_p.py C:kmfeltshapeutm322017%%a_p.shp

...
# Set POINT-shapefile
fn = r""+sys.argv[1]+""   # Read filename from input
print('filnavn er ' +fn)

#get the driver
driver = osgeo.ogr.GetDriverByName('ESRI Shapefile') # will select the driver for our shp-file

# open the data source
dataSource = driver.Open(fn, 1) # 0 means read-only. 1 means writeable (read/write)

# get layer
layer = dataSource.GetLayer()
geotype = layer.GetGeomType()
print(geotype)

...
if layer.GetFeatureCount() == 0:
    km = ogr.FieldDefn('KMNR', ogr.OFTInteger)
    km.SetWidth(4) #4 integer width
    print "Legger til egenskapen KMNR som siste kolonne"
    layer.CreateField(km)
    # After adding fields, get the layer definition
    featureDefn = layer.GetLayerDefn()
    # Create a feature from scratch
    feature = ogr.Feature(featureDefn)
    # Populate the attribute table with a default (dummy) value
    print "Setter KMNR lik 9999"
    feature.SetField("KMNR", 9999)
    # Finally, feature must be written to the layer
    layer.CreateFeature(feature)
    # Clean up memory
    feature.Destroy()