在python中实现try / except语句时无法连接数据库错误

Question

I have a python script below that attempts to make a connection to a sql db. The database was having some issues and I want the script to try to reconnect to the db so I added try / except. Now however I get the error message of "Unable to connect to database". If I take out the try / except statement the script works perfectly. If anyone can help me with getting the try / except statement working I would greatly appreciate it!

Updated code with connection inside of Try

from __future__ import print_function

try:
    import psycopg2
except ImportError:
    raise ImportError('\n\033[33mpsycopg2 library missing. pip install psycopg2\033[1;m\n')
    sys.exit(1)

import re
import sys
import json
import pprint

outfilepath = "crtsh_output/crtsh_flat_file"

DB_HOST = 'crt.sh'
DB_NAME = 'certwatch'
DB_USER = 'guest'

#conn = psycopg2.connect("dbname={0} user={1} host={2}".format(DB_NAME, DB_USER, DB_HOST))
#cursor = conn.cursor()

def connect_to_db():
    filepath = 'forager.txt'
    conn = psycopg2.connect("dbname={0} user={1} host={2}".format(DB_NAME, DB_USER, DB_HOST))
    cursor = conn.cursor()
    with open(filepath) as fp:
        unique_domains = ''
        while True:
            try:
                for cnt, domain_name in enumerate(fp):
                    print("Line {}: {}".format(cnt, domain_name))
                    print(domain_name)
                    domain_name = domain_name.rstrip()

                    cursor.execute('''SELECT c.id, x509_commonName(c.certificate), x509_issuerName(c.certificate), x509_notBefore(c.certificate), x509_notAfter(c.certificate), x509_issuerName(c.certificate)$
                    FROM certificate c, certificate_identity ci WHERE
                    c.id= ci.certificate_id AND ci.name_type = 'dNSName' AND lower(ci.name_value) =
                    lower(%s) AND x509_notAfter(c.certificate) > statement_timestamp()''', (domain_name,))


                    unique_domains = cursor.fetchall()

                    pprint.pprint(unique_domains)

                    outfilepath = "crtsh1" + ".json"
                    with open(outfilepath, 'a') as outfile:
                            outfile.write(json.dumps(unique_domains, sort_keys=True, indent=4, default=str, ensure_ascii = False))
                    break
            except:
                pass
                #print("\n\033[1;31m[!] Unable to connect to the database\n\033[1;m")

if __name__ == "__main__":
    connect_to_db()

Answer 1

You'll want to do a few things:

move this code:

 conn = psycopg2.connect("dbname={0} user={1} host={2}".format(DB_NAME, DB_USER, DB_HOST)) 
 cursor = conn.cursor()

Into your try , that way when it loops if it dies it will remake the connection. Like this:

    try:
        conn = psycopg2.connect("dbname={0} user={1} host={2}".format(DB_NAME, DB_USER, DB_HOST)) 
        cursor = conn.cursor()
        for cnt, domain_name in enumerate(fp):
            print("Line {}: {}".format(cnt, domain_name))
            print(domain_name)
            domain_name = domain_name.rstrip()

I would toss a pause between connections. Your DBA might have code to detect too many connections in a period of time, like this:

#at the top of your code
import time

#in your loop add:
time.sleep(1)