Python/Flask mysql cursor: Why it doesn't work?

user_9004917 0
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from flask import Flask
from flask_mysqldb import MySQL

app = Flask(__name__)
app.config['MYSQL_HOST'] = 'localhost'
app.config['MYSQL_USER'] = 'root'
app.config['MYSQL_PASSWORD'] = 'password'
app.config['MYSQL_DB'] = 'todoapp'
app.config['MYSQL_CURSORCLASS'] = 'DictCursor'
mysql = MySQL(app)
cur = mysql.connection.cursor()

if __name__ == '__main__':
    app.run()

There is error which is displayed after executing program:

cur = mysql.connection.cursor()

AttributeError: 'NoneType' object has no attribute 'cursor'.

According to documentaction it should work. I use Ubuntu 16.04, I have installed MySQL and it works properly. Could anyone explain why it doesn't work?

flask mysql python
5 Answers

You are constructing cursor based on flask_mysqldb , and Flask app won't be constructed itself up until the first route is hit, which means the Flask app will be constructed inside a Flask Function, and that is when your MySQL connection also can be constructed based on your app.config params, and then your cursor can be constructed based on MySQL connection: Flask Construction > MySQL Connection Construction > Cursor Construction.

So you have to use your cursor constructor inside a Flask Function: Instead of:

cur = mysql.connection.cursor()

Put:

@app.route("/")
def index():
   cur = mysql.connection.cursor()
user_120003410

I used the connect() method instead of get_db() and it works with Python 3.5.5. I had the same error when I used get_db

from flask import Flask
from flaskext.mysql import MySQL


app = Flask(__name__)


app.config['MYSQL_DATABASE_USER'] = 'root'
app.config['MYSQL_DATABASE_PASSWORD'] = 'root'
app.config['MYSQL_DATABASE_DB'] = 'test_db'
app.config['MYSQL_DATABASE_HOST'] = 'localhost'

mysql = MySQL()
mysql.init_app(app)

# cursor = mysql.get_db().cursor()
cursor = mysql.connect().cursor()
print(cursor)
user_74551920

The problem is in :

app.config['MYSQL_CURSORCLASS'] = 'DictCursor'

Looking at flaskext.mysql source , that feature is not yet implemented .

And since flaskext.mysql is using pymysql , you can use DictCursor from pymysql.cursors

Example :

from flaskext.mysql import MySQL 
from flask import Flask 
from pymysql import cursors

app=Flask(__name__)

mysql = MySQL(cursorclass=cursors.DictCursor)
mysql.init_app(app)
cursor = mysql.connect().cursor()
user_66233940 
app.config['MYSQL_HOST'] = 'localhost'
app.config['MYSQL_DATABASE_PORT'] = 3308 #here your port

enter image description here

user_132662880

It maybe that you need to init the app for MySQL context.

from flask import Flask
from flask_mysqldb import MySQL

app = Flask(__name__)
mysql = MySQL()
mysql.config['MYSQL_HOST'] = 'localhost'
mysql.config['MYSQL_USER'] = 'root'
mysql.config['MYSQL_PASSWORD'] = 'password'
mysql.config['MYSQL_DB'] = 'todoapp'
mysql.config['MYSQL_CURSORCLASS'] = 'DictCursor'
mysql.init_app(app)
cur = mysql.connection.cursor()

if __name__ == '__main__':
    app.run()
user_67723730
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