Reading in Multiple Variables Python

Question

I have a function I'm trying to execute which calls in 4 different variables:

def listdbtables(dbname, user, host, password):
    try:
        conn = psycopg2.connect("dbname = %s username = %s host = %s pass = %s" % dbname, % user, % host, % password)
        curs = conn.cursor()
        b = curs.execute("\l")
        print b
    except psycopg2.DatabaseError, ex:
        print "I am unable to connect the database: " + ex
        sys.exit(1)

I am unable to read in the variables with my current setup, how do I call in the variables properly in the conn variables.

Edit: Here is the error I am seeing:

      File "./pg_meta.py", line 35
    conn = psycopg2.connect("dbname = %s username = %s host = %s pass = %s" (% dbname, % user, % host, % password))
                                                                             ^
SyntaxError: invalid syntax

chukkwagon · Accepted Answer · 2017-05-01 19:53:31Z

2

try this:

def listdbtables(dbname, user, host, password):
    try:
        conn = psycopg2.connect("dbname = %s username = %s host = %s pass = %s" % (dbname, user, host,password,))
        curs = conn.cursor()
        b = curs.execute("\l")
        print b
    except psycopg2.DatabaseError, ex:
        print "I am unable to connect the database: " + ex
        sys.exit(1)

the format portion needs to be a tuple for multiple values. you should also consider using String.format

answered May 1, 2017 at 19:53

chukkwagon

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Comments

Suraj Nagabhushana Ponnaganti · Accepted Answer · 2017-05-01 19:55:45Z

1

I think this is wrong syntax:

conn = psycopg2.connect("dbname = %s username = %s host = %s pass = %s" % dbname, % user, % host, % password)

Change it to:

conn = psycopg2.connect("dbname = %s username = %s host = %s pass = %s" %(dbname, user, host, password))

another way it to use .format():

conn = psycopg2.connect("dbname = {0} username = {1} host = {2} pass = {3}".format(dbname, user, host, password))

answered May 1, 2017 at 19:55

Suraj Nagabhushana Ponnaganti

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Comments

Chris · Accepted Answer · 2017-05-01 20:10:47Z

1

Your error is saying that you have incorrect syntax in your program. When using the % operator with multiple variables Python requires you to use parenthesis. Change your code to this instead:

conn = psycopg2.connect("dbname = %s username = %s host = %s pass = %s" % (dbname, % user, % host, % password))

However, the recommend way to format variables into strings in newer Python versions would be to use the .format() method, instead of old style string formatting with %:

conn = psycopg2.connect("dbname = {} username = {} host = {} pass = {}".format(
    dbname,  user, host,  password)
)

Both methods have their advantageous and disadvantageous, so I encourage you to find which one works best for you. A good website to compare the two methods is pyformat.info.

edited May 1, 2017 at 20:10

answered May 1, 2017 at 20:03

Chris

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