Develop Reference

Flask error: werkzeug.routing.BuildError when connecting to web service

For educational purposes, we're building a very simple Flask app. While it runs smoothly locally, it no longer does when I copy the code to my virtual private server.
The route is defined as follows:
from flask import Flask, request, render_template
app = Flask(__name__)
#app.route("/", methods=["GET", "POST"])
def sign_up():
...
This is the function that uses autocomplete:
with connection.cursor() as cursor:
sql = f"SELECT * FROM movies WHERE title"
query = cursor.execute(sql)
data = cursor.fetchall()
# from flask import jsonify
results = [data[i]['title'] for i in range(len(data))]
return render_template("autocomplete.html", results=results)
autocomplete.html is located in the templates folder, which sits next to the Python program file.
And the web service is started like this:
if __name__ == '__main__':
app.run(host='0.0.0.0')
I can start the web service successfully, but when I connect using the URL, it returns a 500 error, and the server console shows:
[2020-05-28 16:19:47,099] ERROR in app: Exception on / [GET]
Traceback (most recent call last):
File "/root/miniconda3/lib/python3.7/site-packages/flask/app.py", line 2447, in wsgi_app
response = self.full_dispatch_request()
File "/root/miniconda3/lib/python3.7/site-packages/flask/app.py", line 1952, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/root/miniconda3/lib/python3.7/site-packages/flask/app.py", line 1821, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/root/miniconda3/lib/python3.7/site-packages/flask/_compat.py", line 39, in reraise
raise value
File "/root/miniconda3/lib/python3.7/site-packages/flask/app.py", line 1950, in full_dispatch_request
rv = self.dispatch_request()
File "/root/miniconda3/lib/python3.7/site-packages/flask/app.py", line 1936, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "app.py", line 94, in sign_up
return render_template("autocomplete.html", results=results)
File "/root/miniconda3/lib/python3.7/site-packages/flask/templating.py", line 140, in render_template
ctx.app,
File "/root/miniconda3/lib/python3.7/site-packages/flask/templating.py", line 120, in _render
rv = template.render(context)
File "/root/miniconda3/lib/python3.7/site-packages/jinja2/environment.py", line 1090, in render
self.environment.handle_exception()
File "/root/miniconda3/lib/python3.7/site-packages/jinja2/environment.py", line 832, in handle_exception
reraise(*rewrite_traceback_stack(source=source))
File "/root/miniconda3/lib/python3.7/site-packages/jinja2/_compat.py", line 28, in reraise
raise value.with_traceback(tb)
File "/root/recommender/app-flask/templates/autocomplete.html", line 10, in top-level template code
$.getJSON("{{url_for('autocomplete')}}",{
File "/root/miniconda3/lib/python3.7/site-packages/flask/helpers.py", line 370, in url_for
return appctx.app.handle_url_build_error(error, endpoint, values)
File "/root/miniconda3/lib/python3.7/site-packages/flask/app.py", line 2216, in handle_url_build_error
reraise(exc_type, exc_value, tb)
File "/root/miniconda3/lib/python3.7/site-packages/flask/_compat.py", line 39, in reraise
raise value
File "/root/miniconda3/lib/python3.7/site-packages/flask/helpers.py", line 358, in url_for
endpoint, values, method=method, force_external=external
File "/root/miniconda3/lib/python3.7/site-packages/werkzeug/routing.py", line 2179, in build
raise BuildError(endpoint, values, method, self)
werkzeug.routing.BuildError: Could not build url for endpoint 'autocomplete'. Did you mean 'static' instead?
I assume this is because of a change in the URL, but I don't know how to solve this.
Can anyone help?

$.getJSON("{{url_for('autocomplete')}}",{
=> your code wrong at this line, read more about url_for in flask.
It's need to render route like: <blueprint_name>.<function_name> If use app as route use can skip blueprint_name => Ex: .sign_up
sample

AttributeError: 'NoneType' object has no attribute 'drivername' for Flask Web App

I am currently doing the Python Flask Tutorial by Corey Schafer. In the blueprint video, I'm having trouble with exporting the variables. I have already written to ~/.bash_profile and ~/.profile but it wasn't successful.
In my .profile file:
export SECRET_KEY='5791628bb0b13ce0c676dfde280ba245'
export SQLALCHEMY_DATABASE_URI='sqlite:///sitetest.db'
export EMAIL_USER='email'
export EMAIL_PASS='password'
In my config.py file:
import os
class Config:
SECRET_KEY = os.environ.get('SECRET_KEY')
SQLALCHEMY_DATABASE_URI = os.environ.get('SQLALCHEMY_DATABASE_URI')
MAIL_SERVER = 'smtp.gmail.com'
MAIL_PORT = 587
MAIL_USE_TLS = True
MAIL_USERNAME = os.environ.get('EMAIL_USER')
MAIL_PASSWORD = os.environ.get('EMAIL_PASS')
In my __init__.py file
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_bcrypt import Bcrypt
from flask_login import LoginManager
from flask_mail import Mail
from flaskblog.config import Config
app = Flask(__name__)
app.config.from_object(Config)
db = SQLAlchemy(app)
bcrypt = Bcrypt(app)
login_manager= LoginManager(app)
login_manager.login_view = 'users.login'
login_manager.login_message_category = 'info'
mail = Mail(app)
from flaskblog.users.routes import users
from flaskblog.posts.routes import posts
from flaskblog.main.routes import main
app.register_blueprint(users)
app.register_blueprint(posts)
app.register_blueprint(main)
I have already figured out it is more than likely the variables are not being exported. Any suggestions?
Traceback (most recent call last):
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask/app.py", line 2309, in __call__
return self.wsgi_app(environ, start_response)
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask/app.py", line 2295, in wsgi_app
response = self.handle_exception(e)
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask/app.py", line 1741, in handle_exception
reraise(exc_type, exc_value, tb)
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask/_compat.py", line 35, in reraise
raise value
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask/app.py", line 2292, in wsgi_app
response = self.full_dispatch_request()
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask/app.py", line 1815, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask/app.py", line 1718, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask/_compat.py", line 35, in reraise
raise value
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask/app.py", line 1813, in full_dispatch_request
rv = self.dispatch_request()
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask/app.py", line 1799, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/michael/Flask_Blog/flaskblog/main/routes.py", line 11, in home
posts = Post.query.order_by(Post.date_posted.desc()).paginate(page=page, per_page=5)
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 519, in __get__
return type.query_class(mapper, session=self.sa.session())
File "/home/michael/anaconda3/lib/python3.7/site-packages/sqlalchemy/orm/scoping.py", line 78, in __call__
return self.registry()
File "/home/michael/anaconda3/lib/python3.7/site-packages/sqlalchemy/util/_collections.py", line 1012, in __call__
return self.registry.setdefault(key, self.createfunc())
File "/home/michael/anaconda3/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 3206, in __call__
return self.class_(**local_kw)
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 138, in __init__
bind = options.pop('bind', None) or db.engine
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 937, in engine
return self.get_engine()
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 956, in get_engine
return connector.get_engine()
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 560, in get_engine
options = self.get_options(sa_url, echo)
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 575, in get_options
self._sa.apply_driver_hacks(self._app, sa_url, options)
File "/home/michael/anaconda3/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 877, in apply_driver_hacks
if sa_url.drivername.startswith('mysql'):
AttributeError: 'NoneType' object has no attribute 'drivername'

Are you using a virtual environment for the flask project? Below solution is here just for you.
So when you are using a virtual environment, it works in its own world with its different perks of installed packages. Same works for the environment variable as well. When you are adding your environment variables in the bash_profile and run the project (using virtual environment), it simply do not find the variables. Solution is..
Create an own variable file (say, var_file; as shown below) inside your virtual environment path. Refer below command in the terminal for more clear explanation.
> vim ~/.virtualenvs/your_project_virtual_environment_name/bin/var_file
here the shell file opens up
# add your environment variables
export abc='xyz'
export xyz='wtf'
now exit the file (esc + : + wq!)
> source ~/.virtualenvs/your_project_virtual_environment_name/bin/new_shell_file
Voila..!! Try running the project now. It should work smooth like honey.
Let me know if it works. :)

You need to set a proper DSN for SQLALCHEMY_DATABASE_URI environment variable. It needs to have a valid dialect prefix, like mysql, postgresql, or sqlite, as per docs:
https://docs.sqlalchemy.org/en/13/core/engines.html#database-urls
sa_url.drivername.startswith('mysql'):
This line in the stack trace implies that the DSN you supply is most likely missing a driver name.
Make sure that os.environ.get('SQLALCHEMY_DATABASE_URI') returns a valid DSN.

I'm going through the same tutorial and wrestled a bit with this as well.
I tried adding assert statements to see which environment variable was returning None. Both the SECRET_KEY and DATABASE_URI were giving me trouble. I tried changing the variable names and even removing the quotes.
I'm not exactly quite sure which change solved the issue, but I was able to get the environment variables to work by restarting my terminal.
I hope this helps others in the future.

Flask suddenly not connecting to db

I had a huge working flask application running in an ec2 server with AWS RDS. I am using Apache with mod-wsgi. Suddenly all the URIs which make queries return errors.
I cannot spot why I started getting an "OperationalError: no such table: users u'SELECT users....'
The table is shown in the MySQL show tables. Further if I log into the server, acvitavate the virtualenv, and from the python console run:
from flask.ext.script import Manager
from myapp import create_app
from myapp.extensions import db
app=create_app()
manager=Manager(app)
ctx = app.app_context()
ctx.push()
I can access the user table and others. So what is going on here?
I am using two different configurations (development/production). This is done through the use of an environment variable. If I ran the code above in the production server, then I get the production configuration. How can I start to debug the problematic connection?
The app.wsgi file reads like this
import sys
sys.path.insert(0,"/var/www/myapp")
from myapp import create_app
application = create_app()
and then create_app is called, and apparently it reads the correct configuration. In particular, it will import and run
from flask.ext.sqlalchemy import SQLAlchemy
db = SQLAlchemy()
and then configure it
db.init_app(app)
The apache2 error log reads like this:
mod_authz_core.c(802): [client XXX.XX.XX.XX:29629] AH01626: authorization result of Require all granted: granted
mod_authz_core.c(802): [client XXX.XX.XX.XX:29629] AH01626: authorization result of <RequireAny>: granted
mod_authz_core.c(802): [client XXX.XX.XX.XX:29629] AH01626: authorization result of Require all granted: granted
mod_authz_core.c(802): [client XXX.XX.XX.XX:29629] AH01626: authorization result of <RequireAny>: granted
mod_wsgi (pid=6780, process='', application='ec2-XXX.XX.XX.XX.compute-1.amazonaws.com|'): Reloading WSGI script '/var/www/wsgi-scripts/app.wsgi'.
mod_wsgi (pid=6780): Exception occurred processing WSGI script '/var/www/wsgi-scripts/app.wsgi'.
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/Flask-0.10.1-py2.7.egg/flask/app.py", line 1836, in __call__
return self.wsgi_app(environ, start_response)
File "/usr/local/lib/python2.7/dist-packages/Flask-0.10.1-py2.7.egg/flask/app.py", line 1820, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/usr/local/lib/python2.7/dist-packages/Flask-0.10.1-py2.7.egg/flask/app.py", line 1403, in handle_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python2.7/dist-packages/Flask-0.10.1-py2.7.egg/flask/app.py", line 1817, in wsgi_app
response = self.full_dispatch_request()
File "/usr/local/lib/python2.7/dist-packages/Flask-0.10.1-py2.7.egg/flask/app.py", line 1477, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/usr/local/lib/python2.7/dist-packages/Flask-0.10.1-py2.7.egg/flask/app.py", line 1381, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python2.7/dist-packages/Flask-0.10.1-py2.7.egg/flask/app.py", line 1475, in full_dispatch_request
rv = self.dispatch_request()
File "/usr/local/lib/python2.7/dist-packages/Flask-0.10.1- py2.7.egg/flask/app.py", line 1461, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/var/www/myapp/myapp/frontend/views.py", line 71, in index
#current_app.logger.debug('debug')
File "/usr/local/lib/python2.7/dist-packages/Flask_SQLAlchemy-2.0- py2.7.egg/flask_sqlalchemy/__init__.py", line 431, in paginate
items = self.limit(per_page).offset((page - 1) * per_page).all()
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7- linux-x86_64.egg/sqlalchemy/orm/query.py", line 2320, in all
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7- linux-x86_64.egg/sqlalchemy/orm/query.py", line 2438, in __iter__
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7-linux-x86_64.egg/sqlalchemy/orm/query.py", line 2453, in _execute_and_instances
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7-linux-x86_64.egg/sqlalchemy/engine/base.py", line 729, in execute
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7-linux-x86_64.egg/sqlalchemy/sql/elements.py", line 322, in _execute_on_connection
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7-linux-x86_64.egg/sqlalchemy/engine/base.py", line 826, in _execute_clauseelement
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7-linux-x86_64.egg/sqlalchemy/engine/base.py", line 958, in _execute_context
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7-linux-x86_64.egg/sqlalchemy/engine/base.py", line 1159, in _handle_dbapi_exception
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7-linux-x86_64.egg/sqlalchemy/util/compat.py", line 199, in raise_from_cause
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7-linux-x86_64.egg/sqlalchemy/engine/base.py", line 951, in _execute_context
File "/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.9.8-py2.7-linux-x86_64.egg/sqlalchemy/engine/default.py", line 436, in do_execute
OperationalError: (OperationalError) no such table: users u'SELECT users.password AS users_password, users.id AS users_id, users.name AS users_name, users.email AS users_email, users.openid AS users_openid, users.activation_key AS users_activation_key, users.created_time AS users_created_time, users.avatar AS users_avatar, users.role_code AS users_role_code, users.status_code AS users_status_code, users.user_detail_id AS users_user_detail_id, users.followers AS users_followers, users.following AS users_following \\nFROM users\\n LIMIT ? OFFSET ?' (10, 0)

There was a sequence of details that led to the problem. By design, the default configuration is loaded first and then it is overwritten with the line
app.config.from_envvar("PRODUCTION_CFG",silent=True)
The problem was that the environment variable was set in the session in which I was using the bash, but not in the session were the server was running. I fixed it by using app.config.from_pyfile instead.

Flask-SQLAlchemy with Google App Engine only works in interactive console

I am trying to get my Google App Engine app to work with Flask-SQLAlchemy. I am getting the error:
AttributeError: 'module' object has no attribute 'paramstyle'
I have followed the instructions in this answer (Local MySQLdb connection fails with AttributeError for paramstyle when running GAE development server) and so I no longer get the error in the interactive console (when I make an app context).
However, the error still appears when I run the app in my local GAE. Why is this still happening? I am running OSX Mavericks. The full trace:
Traceback (most recent call last):
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/runtime/wsgi.py", line 266, in Handle
result = handler(dict(self._environ), self._StartResponse)
File "/Users/conor/Documents/Projj/lib/flask/app.py", line 1836, in __call__
return self.wsgi_app(environ, start_response)
File "/Users/conor/Documents/Projj/lib/flask/app.py", line 1820, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/Users/conor/Documents/Projj/lib/flask/app.py", line 1403, in handle_exception
reraise(exc_type, exc_value, tb)
File "/Users/conor/Documents/Projj/lib/flask/app.py", line 1817, in wsgi_app
response = self.full_dispatch_request()
File "/Users/conor/Documents/Projj/lib/flask/app.py", line 1477, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/Users/conor/Documents/Projj/lib/flask/app.py", line 1381, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/Users/conor/Documents/Projj/lib/flask/app.py", line 1475, in full_dispatch_request
rv = self.dispatch_request()
File "/Users/conor/Documents/Projj/lib/flask/app.py", line 1461, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/Users/conor/Documents/Projj/financey.py", line 117, in login_view
userObj = get_user(username)
File "/Users/conor/Documents/Projj/financey.py", line 88, in get_user
return db.session.query(User).filter_by(username=username).first()
File "/Users/conor/Documents/Projj/lib/sqlalchemy/orm/scoping.py", line 149, in do
return getattr(self.registry(), name)(*args, **kwargs)
File "/Users/conor/Documents/Projj/lib/sqlalchemy/util/_collections.py", line 864, in __call__
return self.registry.setdefault(key, self.createfunc())
File "/Users/conor/Documents/Projj/lib/flask_sqlalchemy/__init__.py", line 139, in __init__
bind=db.engine,
File "/Users/conor/Documents/Projj/lib/flask_sqlalchemy/__init__.py", line 780, in engine
return self.get_engine(self.get_app())
File "/Users/conor/Documents/Projj/lib/flask_sqlalchemy/__init__.py", line 797, in get_engine
return connector.get_engine()
File "/Users/conor/Documents/Projj/lib/flask_sqlalchemy/__init__.py", line 473, in get_engine
self._engine = rv = sqlalchemy.create_engine(info, **options)
File "/Users/conor/Documents/Projj/lib/sqlalchemy/engine/__init__.py", line 332, in create_engine
return strategy.create(*args, **kwargs)
File "/Users/conor/Documents/Projj/lib/sqlalchemy/engine/strategies.py", line 69, in create
dialect = dialect_cls(**dialect_args)
File "/Users/conor/Documents/Projj/lib/sqlalchemy/dialects/mysql/base.py", line 1985, in __init__
default.DefaultDialect.__init__(self, **kwargs)
File "/Users/conor/Documents/Projj/lib/sqlalchemy/engine/default.py", line 124, in __init__
self.paramstyle = self.dbapi.paramstyle
AttributeError: 'module' object has no attribute 'paramstyle'
EDIT: In attempting to further diagnose the issue, when I import MySQLdb in the GAE Interactive Console (in the browser) I get the error ImportError: No module named _mysql

After looking around and debugging for far too long, I finally discovered the issue. When you run the GAE development server, the dev_appserver must be told exactly which MySQL instance you want to connect to. The connection string you use (e.g. in Python) doesn't matter. The connection string only determines database name and instance. However, SQLAlchemy can figure it out fine if you run form an ipython console. This may be due to a different driver being used under the hood.
Hopefully this saves someone else a lot of hair-pulling. Run your dev_appserver.py like so:
dev_appserver.py --mysql_host=<Cloud SQL IP> --mysql_user=root --mysql_password=<Cloud SQL root password> <application directory>

Pyimgur code works on Windows, not on Ubuntu

I have a simple code that creates an album in imgur, via pyimgur. This is the code:
#app.route('/get_album')
def get_album():
im = pyimgur.Imgur(CLIENT_ID)
new_album = im.create_album()
return new_album.link
(I tried with im = pyimgur.Imgur(CLIENT_ID) line before the route handlers as well, same thing happens)
On Windows, everything is perfectly fine. However, when I upload the code to my VPS, I get the following error when I try to do something with the api:
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1836, in __ca ll__
return self.wsgi_app(environ, start_response)
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1820, in wsgi _app
response = self.make_response(self.handle_exception(e))
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1403, in hand le_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1817, in wsgi _app
response = self.full_dispatch_request()
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1477, in full _dispatch_request
rv = self.handle_user_exception(e)
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1381, in hand le_user_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1475, in full _dispatch_request
rv = self.dispatch_request()
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1461, in disp atch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/api/imgur.py", line 161, in get_album_link
new_album = im.create_album()
File "/usr/local/lib/python2.7/dist-packages/pyimgur-0.4.2-py2.7.egg/pyimgur/_ _init__.py", line 754, in create_album
resp = self._send_request(url, params=payload, method='POST')
File "/usr/local/lib/python2.7/dist-packages/pyimgur-0.4.2-py2.7.egg/pyimgur/_ _init__.py", line 687, in _send_request
result = request.send_request(url, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/pyimgur-0.4.2-py2.7.egg/pyimgur/r equest.py", line 91, in send_request
content = resp.json()
TypeError: 'dict' object is not callable
I updated flask to the latest version, and I've been using pyimgur 4, latest release I got from github (pip install doesnt work so I had to install it manually, on both Windows and Ubuntu, since some error about setup.py pops out. I used python setup.py install command)

OK, so I have found a solution. The solution was a change in requests module, which probably came along with updated flask or something, so the old method didn't behave like it used to. I updated the requests as well on my VPS (forgot to do it when upgrading flask), and the issue is now solved.