unable to call shp2pgsql using python

Question

I am unable to call shp2pgsql using python as I have to pass various options like (-s -a -i) and I am not getting the required output ..

Method I am using is

p1 = subprocess.Popen(["cmd", "/C", "shp2pgsql","-a","-s 4326","roads.shp" "roads", ">","roads.sql"],stdout=subprocess.PIPE)

>>>p1.communicate()[0]

as my intension is to add the features of the shapefile into the already existing table in the database

I am done with the environment settings.. roads.shp is the name of the shapefile roads is the table name and roads.sql is the sql file name..

Answer 1

This seems a bit convoluted. Why not use os.system instead? Just write out / manipulate the command as a string and feed it to os.system.

Answer 2

I suggest you can use the following codes:

p1 = subprocess.Popen(["cmd", "/C", "shp2pgsql","-a","-s 4326","roads.shp" "roads"], stdout=subprocess.PIPE)
stdout, stderr = p1.communicate()
with open('roads.sql', 'w') as f:
    f.writelines(stdout)
    f.close()

Another alternative method (if you want to import this into postgresql database):

p1 = subprocess.Popen(["cmd", "/C", "shp2pgsql","-a","-s 4326","roads.shp" "roads"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
p2 = subprocess.Popen(['psql',  '-d db'], stdin=p1.stdout, 
    stdout=subprocess.PIPE, stderr=subprocess.PIPE)
p1.stdout.close()
stdout, stderr= p2.communicate()

References:

1. http://docs.python.org/2/library/subprocess.html#subprocess.Popen.communicate
2. http://docs.python.org/2/library/subprocess.html#replacing-shell-pipeline