3

I use driving_distance in postgresql to find distances between all nodes, and here's my python script in pyscripter,

import sys

#set up psycopg2 environment
import psycopg2

#driving_distance module
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
    )
;"""

#make connection between python and postgresql
conn = psycopg2.connect("dbname = 'routing_template' user = 'postgres' host = 'localhost' password = 'ntubse40'")
cur = conn.cursor()

#count rows in the table
cur.execute("select count(*) from network")
result = cur.fetchone()
k = result[0] + 1

#run loops
rs = []
i = 1
while i <= k:
    cur.execute(query, (i, 1000000, False, False))
    rs.append(cur.fetchall())
    i = i + 1

#print result
for record in rs:
    print record
conn.close()

The result is fine, and part of the it in python interpreter looks like this,

[(1, 2, 35789.4069722436), (2, 2, 31060.0761437413), (3, 19, 30915.1312550546), (4, 3, 33438.0715007666), (5, 4, 29149.0894812718), (6, 7, 25504.020006665), (7, 7, 29594.741802956), (8, 5, 20736.2427352646), (9, 10, 19545.809601197), (10, 8, 22609.5146670393), (11, 9, 14134.5400189648), (12, 11, 12266.7845493204), (13, 18, 17426.7449057031), (14, 21, 11754.7277029158), (15, 18, 13128.3548040769), (16, 20, 21924.2253916803), (17, 11, 15209.9969992088), (18, 20, 26316.7797545076), (19, 13, 604.414419026164), (20, 16, 740.652673783403), (21, 15, 0.0), (22, 15, 2378.768084459)]
[(1, 2, 38168.1750567026), (2, 2, 33438.8442282003), (3, 19, 33293.8993395136), (4, 3, 35816.8395852256), (5, 4, 31527.8575657308), (6, 7, 27882.788091124), (7, 7, 31973.509887415), (8, 5, 23115.0108197236), (9, 10, 21924.577685656), (10, 8, 24988.2827514983), (11, 9, 16513.3081034238), (12, 11, 14645.5526337793), (13, 18, 19805.5129901621), (14, 21, 14133.4957873748), (15, 18, 15507.1228885359), (16, 20, 24302.9934761393), (17, 11, 17588.7650836678), (18, 20, 28695.5478389666), (19, 13, 2983.18250348516), (20, 16, 3119.4207582424), (21, 15, 2378.768084459), (22, 15, 0.0)]

I want to export these results to a new csv or excel files, and I have looked these related post and website,

But still can't export these working under pyscripter, how can I do?

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

5

This is really just a Python question. Use the csv module in Python to write your output (https://docs.python.org/2/library/csv.html)

import csv

records = [(1, 2, 3), (4, 5, 6), (7, 8, 9)]

with open('somefile.csv', 'w') as f:
    writer = csv.writer(f, delimiter=',')
    for row in records:
        writer.writerow(row)

print "Done Writing"
1
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
    )
;"""
outputquery = "COPY ({0}) TO STDOUT WITH CSV HEADER".format(query)
with open('archivo.csv', 'w') as f:
    cur.copy_expert(outputquery, f)
conn.close()
  • I got some error message : 'No such file or directory' shouldn't the with open take care of this ? – Basile Aug 9 at 10:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.