如何修复“”AttributeError: 'NoneType' 对象没有属性 'app'

Question

I am new to web framework and I am trying to do a simple project. I want to display MySQL data on an html page however I keep getting this AttributeError: 'NoneType' object has no attribute 'app'.

I have looked at other solutions but I can't seem to figure out what I am doing wrong. Any help would be appreciated. I did run the this code:

TEST.py

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, World!'

print(hello_world())

and this ran fine.

python code

import mysql.connector
from flask import Flask, render_template
app = Flask(__name__)

hostname = ''
username = ''
password = ''
database = ''

#run query on a database
@app.route('/')
def doQuery(conn):
    cur = conn.cursor()
    query = "SELECT * FROM maxes"
    cur.execute(query)

    data = cur.fetchall()

    return render_template("weightlifting.html", data=data)

print("Using mysql.connector")
myConnection = mysql.connector.connect(host=hostname, user=username, password=password, db=database)
doQuery(myConnection)
myConnection.close()

This is the error that I am getting:

Using mysql.connector
Traceback (most recent call last):
  File "database.py", line 24, in <module>
    doQuery(myConnection)
  File "database.py", line 20, in doQuery
    return render_template("weightlifting.html", data=data)
  File "C:\Users\kbb_n\Anaconda3_2\lib\site-packages\flask\templating.py", line 133, in render_template
    ctx.app.update_template_context(context)
AttributeError: 'NoneType' object has no attribute 'app'

Answer 1

In general, you aren't really supposed to directly call the route functions.

Your hello_world test just happened to work because that view returns a simple string.

But the doQuery view returns a template render, which is more complicated and requires an actual web request context, which is missing when you just call the function directly.

Answer 2

I was getting a similar error when trying to run Python code on Google's AppEngine. The solution was using app.config.update() to specify the server. I used SERVER_NAME to do this:

app.config.update(
    SERVER_NAME = "127.0.0.1:8080"
)