How to execute sql lines in postgresql using python？

Question

I use postgresql 8.4 to route a river network, the following is my code typed in pgAdmin and the result is fine,

select * from driving_distance
('select gid as id,
 start_id::int4 as source, end_id::int4 as target,
 shape_leng::double precision as cost from network',
 10, 1000000, false, false);

I have installed psycopg2 and it successfully connect python and postgresql,

#set up python and postgresql connection
import psycopg2

try:
    conn = psycopg2.connect("dbname = 'routing_template' user = 'postgres' host = 'localhost' password = 'xxxxx'")
except:
    print 'I am unable to connect the database'

Now I need to directly execute my sql code on the top in pyscripter, how should I change these codes to python code？

I am working with postgresql 8.4, python 2.7.6 under Windows 8.1 x64.

Answer 1

Use the execute method of the cursor class to pass the parameters

import psycopg2

query = """
    select *
    from driving_distance ($$
        select
            gid as id,
            start_id::int4 as source,
            end_id::int4 as target,
            shape_leng::double precision as cost
        from network
        $$, %s, %s, %s, %s
    )
;"""


conn = psycopg2.connect("dbname=cpn")
cur = conn.cursor()
cur.execute(query, (10, 1000000, False, False))
rs = cur.fetchall()
conn.close()
print rs

Notice the use of triple quotes in Python and Dollar-quoted String Constants in the SQL code