ogr2ogr -update -append -f PostgreSQL PG:"dbname=geodb user=postgres password=admin" myshp.shp -nln existing_table

import os
import process
cmd='ogr2ogr -update -append -f PostgreSQL PG:"dbname=geodb host=localhost port=5432 user=postgres password=admin" myshp.shp -nln existing_table'
input_command = [cmd]
program='C:/Program Files (x86)/FWTools2.4.7/bin/ogr2ogr.exe'
command_run = subprocess.call([program, input_command])
if command_run == 0:
    print "Its worked!!"
else:
    print 'no'