Flask & Alchemy - (psycopg2.OperationalError) FATAL: password authentication failed - postgresql

Question

I'm new to python. I have to develop a simple Flask app (in my local Ubuntu 16.4) with PostgreSQL as database.
I install pgadmin, Flask, SQLAlchemy and postgres and also this is my app code:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://dbUserName:userNamePassword#localhost/dbName'
db = SQLAlchemy(app)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(80), unique=True)
email = db.Column(db.String(120), unique=True)
def __init__(self, username, email):
self.username = username
self.email = email
def __repr__(self):
return '<User %r>' % self.username
#app.route('/')
def index():
return "Hello Flask"
if __name__ == "__main__":
app.run()
Also I create a database and new user in pgAdmin (and replace them with related variable in my code), but when I try to test this code in python shell I found error.
my python code:
from app import db
result:
/home/user/point2map2/venv/lib/python3.5/site-packages/flask_sqlalchemy/__init__.py:839: FSADeprecationWarning: SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future. Set it to True or False to suppress this warning.
'SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and '
Then:
db.create_all()
result:
(psycopg2.OperationalError) FATAL: password authentication failed for user "dbUserName"
FATAL: password authentication failed for user "dbUserName"
after a lot of search in forum I found this guide:
in your pg_hba.conf
# IPv4 local connections:
# TYPE DATABASE USER CIDR-ADDRESS METHOD
host all all 127.0.0.1/32 trust
But its not work for me.

Answer 1

I was stuck with this same error.
The problem for me was that I hadn't set the password for the psql user.
See similar question with answer here:
https://askubuntu.com/questions/413585/postgres-password-authentication-fails
it got solved when I did
ALTER USER db_username PASSWORD 'new_password'

Answer 2

its an old question and i guess its not important to you but for people with same problem in future:
i was stuck too. i found postgres default behavior converts everything to lowercase.[1]
my problem solved when i converted my user to lowercase.
sorry for bad english :(

Answer 3

After some debugging of my sqlalchemy code, I saw that the url that sqlalchemy used was a decoded url-string (at least for postgres). This means that if you have substrings in your connection string such as %34, the sqlalchemy connection string will be 4, as that is the url-decoded string. The solution for this problem is simple: simply replace all occurences of % in the connection string with %25, as that is the url encoding for %. The code for this is simply:
from sqlalchemy import create_engine
connection_string_orig = "postgres://user_with_%34_in_the_string:pw#host:port/db"
connection_string = connection_string_orig.replace("%", "%25")
engine = create_engine(connection_string)
print(engine.url) # should be identical to connection_string_orig
engine.connect()
This probably doesn't solve everyone's problem, but it's nevertheless good to be aware of it.