Evaluate postgres boolean field

[andydtaylor]

Hi,

I'm hoping for some help on a python script I need to query an api. I'm not a (Python) programmer ordinarily, but do plan to improve!

Specifically I have a for loop evaluating a database row, which I think I can treat as a list. My [4] is a postgres boolean field, and I'm temporarily stuck on how to evaluate this to determine if I use the values in [1].

Could I have some advice on what to change? Also do let me know if you can recommend a good beginners python book.

Data example:

[13, 'Barbican Station', 'Barbican Station, London Underground Ltd., Aldersgate St, London, EC1A 4JA', '01010000E0E61000008851AB9E9803B9BF5BB6972294C2494000000000000000000000000000000000', True]


Code:

#!/usr/bin/python
import psycopg2
#note that we have to import the Psycopg2 extras library!
import psycopg2.extras
import sys

def main():
conn_string = "host='localhost' dbname='gisdb' user='postgres' password='#########'"
# print the connection string we will use to connect
print "Connecting to database\n ->%s" % (conn_string)

conn = psycopg2.connect(conn_string)

# HERE IS THE IMPORTANT PART, by specifying a name for the cursor
# psycopg2 creates a server-side cursor, which prevents all of the
# records from being downloaded at once from the server.
cursor = conn.cursor('cursor_tube', cursor_factory=psycopg2.extras.DictCursor)
cursor.execute('SELECT * FROM tubestations LIMIT 1000')

# Because cursor objects are iterable we can just call 'for - in' on
# the cursor object and the cursor will automatically advance itself
# each iteration.
# This loop should run 1000 times, assuming there are at least 1000
# records in 'my_table'
row_count = 0
for row in cursor:
row_count += 1
if row[4] = True
print row[1]
#print "row: %s %s\n" % (row_count, row)

if __name__ == "__main__":
main()



Thanks!


Andy

 

[donarb]

Hi,

I'm hoping for some help on a python script I need to query an api. I'm not a (Python) programmer ordinarily, but do plan to improve!

Specifically I have a for loop evaluating a database row, which I think Ican treat as a list. My [4] is a postgres boolean field, and I'm temporarily stuck on how to evaluate this to determine if I use the values in [1].

Could I have some advice on what to change? Also do let me know if you can recommend a good beginners python book.

Data example:

[13, 'Barbican Station', 'Barbican Station, London Underground Ltd., Aldersgate St, London, EC1A 4JA', '01010000E0E61000008851AB9E9803B9BF5BB6972294C2494000000000000000000000000000000000', True]


Code:

#!/usr/bin/python
import psycopg2
#note that we have to import the Psycopg2 extras library!
import psycopg2.extras
import sys

def main():
conn_string = "host='localhost' dbname='gisdb' user='postgres' password='#########'"
# print the connection string we will use to connect
print "Connecting to database\n ->%s" % (conn_string)

conn = psycopg2.connect(conn_string)

# HERE IS THE IMPORTANT PART, by specifying a name for the cursor
# psycopg2 creates a server-side cursor, which prevents all of the
# records from being downloaded at once from the server.
cursor = conn.cursor('cursor_tube', cursor_factory=psycopg2.extras.DictCursor)
cursor.execute('SELECT * FROM tubestations LIMIT 1000')

# Because cursor objects are iterable we can just call 'for - in' on
# the cursor object and the cursor will automatically advance itself
# each iteration.
# This loop should run 1000 times, assuming there are at least 1000
# records in 'my_table'
row_count = 0
for row in cursor:
row_count += 1
if row[4] = True
print row[1]
#print "row: %s %s\n" % (row_count, row)

if __name__ == "__main__":
main()

Thanks!


Andy

Your code is pretty close to working, you just need to make a couple modifications. You are using the equals sign as an assignment, not a comparison, although the comparison and value are unnecessary since the field's value is either true or false. And you're missing a colon at the end of the condition. Note also that since you are using a DictCursor you can use column names to reference your row's fields, I guessed on the field names, but you should get the idea.


for row in cursor:
row_count += 1
if row['active']:
print row['name']

 

[John Gordon]

for row in cursor:
row_count += 1
if row[4] = True
print row[1]

Since row[4] is a boolean value, you should be able to just say:

if row[4]:
print row[1]

 

[andydtaylor]

Brilliant, thanks guys