Connecting python and mariadb return error 'local variable 'mariadb_connection' referenced before assignment'

Question

I'm running python to connect to mariadb sql and do database create, table create and insert data. I'm getting error

local variable 'mariadb_connection' referenced before assignment

I follow the code below.

import mysql.connector as mariadb

def dbconnect():
    try:
        mariadb_connection = mariadb.connect(
            host="192.168.100.115",
            user="usr1",
            password="usr1",
            database="mydb",
        )
    except Exception as e:
        sys.exit("Can't connect to Database")
    return mariadb_connection

def create_db(db_name, table_name):
    try:
        mariadb_connection = dbconnect()
        cursor = mariadb_connection.cursor()

        # Create Database:
        cursor.execute("CREATE DATABASE IF NOT EXISTS {}".format(db_name))
        cursor.execute(
        """CREATE TABLE IF NOT EXISTS {}.{}(id INT primary key auto_increment, ser_num int(20), log_stat varchar(50), descrp varchar(50));""".format(db_name, table_name))

        with open(latestFile, 'r') as f:
             data = json.load(f)


        sql = "INSERT INTO `table1` (`ser_num`, `log_stat`, `descrp`) VALUES ( %(ser_num)s, %(log_stat)s, %(descrp)s )"
        cursor.executemany( sql, data['response']['data_log']['data'])

        mariadb_connection.commit()
        mariadb_connection.close()

    except Exception as e:
        print e

I really appreciate someone could advise me what is the problem to resolve... I have tried for few days without any luck. Please help me. Thank you for your support and help.

#

After updated above as per comment by bruno.... i can run the script but it return error '1044 (42000): Access denied for user 'usr1'@'%' to database 'mydb'.. usr1 have read/write privilege

bruno desthuilliers · Accepted Answer · 2020-03-18 11:59:11Z

1

Here:

mariadb_connection = mariadb_connection()

Python has no variable declaration statement, so assignment creates a local variable. This shadows any other global by the same name (note that Python doesn't have distinct namespaces for functions or classes either since everything is an object including functions etc), so you are indeed referencing mariadb_connection (on the rhs) before assignment (since the rhs is eval'd before the result is bound to the name).

Now your function is named dbconnect, not mariadb_connection so the fix is quite easy: just replace this line with

mariadb_connection = dbconnect()

NB : If your function had been named mariadb_connection, you would have needed to rename either the function or the variable - the point is that you can not assign the result of a function call to a local variable by the same name as the function, period.

As a side note, you should remove those try/except blocks, they're doing more harm than good by hiding the very useful debugging informations contained in the traceback. As a general rule, only catch exception that you can properly handle.

edited Mar 18, 2020 at 11:59

answered Mar 18, 2020 at 11:11

bruno desthuilliers

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8 Comments

chenoi Over a year ago

Hi sir... thanks for your notes... I'm still try to understand python sql ... do i need to remove 'mariadb_connection = mariadb_connection()'? .... .. i tried remove it and change 'dbconnect' to 'mariadb_connection' function name.. still learning it... thanks for your support

bruno desthuilliers Over a year ago

@chenoi yes, you have to replace mariadb_connection = mariadb_connection() with mariadb_connection = dbconnect()

bruno desthuilliers Over a year ago

Alos note that this has nothing to do with mariadb nor sql nor json - it's purely a Python, syntax issue.

chenoi Over a year ago

Noted...I can see my mistake... i didnt point to the right function ' dbconnect()'...

bruno desthuilliers Over a year ago

You actually would have got the very same error if your function had been named 'mariadb_connection` - you then would have needed to change either the function name or the variable name.

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