sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) fe_sendauth: no password supplied - postgresql

Question

i am trying to run this simple flask app and I keep getting this error in the terminal when trying to run the flask app
FLASK_APP=app.py flask run
i keep getting this error :
sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) fe_sendauth: no password supplied
here is my app:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://postgres#localhost:5432/testdb'
db = SQLAlchemy(app)
class Person(db.Model):
__tablename__ = 'persons'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(), nullable=False)
db.create_all()
#app.route('/')
def index():
return 'Hello World!'
just to clarify i have psycopg2, flask-SQLAlchemy and all dependencies installed AND THERE IS NO PASSWORD FOR USER postgres by default and i haven't changed that and i can log in to database as postgres using psql without password without any problems.
Full error output:
FLASK_APP=app.py flask run
* Serving Flask app "app.py"
* Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
Use a production WSGI server instead.
* Debug mode: off
/usr/lib/python3/dist-packages/flask_sqlalchemy/__init__.py:800: UserWarning: SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future. Set it to True to suppress this warning.
warnings.warn('SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future. Set it to True to suppress this warning.')
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 1122, in _do_get
return self._pool.get(wait, self._timeout)
File "/usr/lib/python3/dist-packages/sqlalchemy/util/queue.py", line 145, in get
raise Empty
sqlalchemy.util.queue.Empty
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/base.py", line 2147, in _wrap_pool_connect
return fn()
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 387, in connect
return _ConnectionFairy._checkout(self)
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 766, in _checkout
fairy = _ConnectionRecord.checkout(pool)
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 516, in checkout
rec = pool._do_get()
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 1138, in _do_get
self._dec_overflow()
File "/usr/lib/python3/dist-packages/sqlalchemy/util/langhelpers.py", line 66, in __exit__
compat.reraise(exc_type, exc_value, exc_tb)
File "/usr/lib/python3/dist-packages/sqlalchemy/util/compat.py", line 187, in reraise
raise value
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 1135, in _do_get
return self._create_connection()
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 333, in _create_connection
return _ConnectionRecord(self)
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 461, in __init__
self.__connect(first_connect_check=True)
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 651, in __connect
connection = pool._invoke_creator(self)
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/strategies.py", line 105, in connect
return dialect.connect(*cargs, **cparams)
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/default.py", line 393, in connect
return self.dbapi.connect(*cargs, **cparams)
File "/home/aa/.local/lib/python3.6/site-packages/psycopg2/__init__.py", line 126, in connect
conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
psycopg2.OperationalError: fe_sendauth: no password supplied
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/home/aa/.local/bin/flask", line 11, in <module>
sys.exit(main())
File "/home/aa/.local/lib/python3.6/site-packages/flask/cli.py", line 967, in main
cli.main(args=sys.argv[1:], prog_name="python -m flask" if as_module else None)
File "/home/aa/.local/lib/python3.6/site-packages/flask/cli.py", line 586, in main
return super(FlaskGroup, self).main(*args, **kwargs)
File "/home/aa/.local/lib/python3.6/site-packages/click/core.py", line 782, in main
rv = self.invoke(ctx)
File "/home/aa/.local/lib/python3.6/site-packages/click/core.py", line 1259, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/home/aa/.local/lib/python3.6/site-packages/click/core.py", line 1066, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/home/aa/.local/lib/python3.6/site-packages/click/core.py", line 610, in invoke
return callback(*args, **kwargs)
File "/home/aa/.local/lib/python3.6/site-packages/click/decorators.py", line 73, in new_func
return ctx.invoke(f, obj, *args, **kwargs)
File "/home/aa/.local/lib/python3.6/site-packages/click/core.py", line 610, in invoke
return callback(*args, **kwargs)
File "/home/aa/.local/lib/python3.6/site-packages/flask/cli.py", line 848, in run_command
app = DispatchingApp(info.load_app, use_eager_loading=eager_loading)
File "/home/aa/.local/lib/python3.6/site-packages/flask/cli.py", line 305, in __init__
self._load_unlocked()
File "/home/aa/.local/lib/python3.6/site-packages/flask/cli.py", line 330, in _load_unlocked
self._app = rv = self.loader()
File "/home/aa/.local/lib/python3.6/site-packages/flask/cli.py", line 388, in load_app
app = locate_app(self, import_name, name)
File "/home/aa/.local/lib/python3.6/site-packages/flask/cli.py", line 240, in locate_app
__import__(module_name)
File "/home/aa/Desktop/Udacity - FullStackND 2020/FullStackND2020/Practice Projects/flask hello world app/app.py", line 18, in <module>
db.create_all()
File "/usr/lib/python3/dist-packages/flask_sqlalchemy/__init__.py", line 972, in create_all
self._execute_for_all_tables(app, bind, 'create_all')
File "/usr/lib/python3/dist-packages/flask_sqlalchemy/__init__.py", line 964, in _execute_for_all_tables
op(bind=self.get_engine(app, bind), **extra)
File "/usr/lib/python3/dist-packages/sqlalchemy/sql/schema.py", line 3934, in create_all
tables=tables)
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/base.py", line 1928, in _run_visitor
with self._optional_conn_ctx_manager(connection) as conn:
File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
return next(self.gen)
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/base.py", line 1921, in _optional_conn_ctx_manager
with self.contextual_connect() as conn:
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/base.py", line 2112, in contextual_connect
self._wrap_pool_connect(self.pool.connect, None),
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/base.py", line 2151, in _wrap_pool_connect
e, dialect, self)
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/base.py", line 1465, in _handle_dbapi_exception_noconnection
exc_info
File "/usr/lib/python3/dist-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause
reraise(type(exception), exception, tb=exc_tb, cause=cause)
File "/usr/lib/python3/dist-packages/sqlalchemy/util/compat.py", line 186, in reraise
raise value.with_traceback(tb)
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/base.py", line 2147, in _wrap_pool_connect
return fn()
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 387, in connect
return _ConnectionFairy._checkout(self)
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 766, in _checkout
fairy = _ConnectionRecord.checkout(pool)
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 516, in checkout
rec = pool._do_get()
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 1138, in _do_get
self._dec_overflow()
File "/usr/lib/python3/dist-packages/sqlalchemy/util/langhelpers.py", line 66, in __exit__
compat.reraise(exc_type, exc_value, exc_tb)
File "/usr/lib/python3/dist-packages/sqlalchemy/util/compat.py", line 187, in reraise
raise value
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 1135, in _do_get
return self._create_connection()
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 333, in _create_connection
return _ConnectionRecord(self)
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 461, in __init__
self.__connect(first_connect_check=True)
File "/usr/lib/python3/dist-packages/sqlalchemy/pool.py", line 651, in __connect
connection = pool._invoke_creator(self)
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/strategies.py", line 105, in connect
return dialect.connect(*cargs, **cparams)
File "/usr/lib/python3/dist-packages/sqlalchemy/engine/default.py", line 393, in connect
return self.dbapi.connect(*cargs, **cparams)
File "/home/aa/.local/lib/python3.6/site-packages/psycopg2/__init__.py", line 126, in connect
conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) fe_sendauth: no password supplied

Answer 1

Other than just setting a password, you can log in without a password by:
Enable trust authentication, eg echo "local all all trust" | sudo tee -a /etc/postgresql/10/main/pg_hba.conf
Create a role with login access with the same username as your local username, eg if whoami returns myname, then sudo -u postgres psql -c "CREATE ROLE myname WITH LOGIN"
Use sqlalchemy's postgresql unix domain connection instead of tcp (ref), eg "postgres+psycopg2://myname#/mydb"
Note that this requires installing pip3 install psycopg2-binary

Answer 2

so apparently you need a password to connect to database from SQLAlchemy, I was able to work around this by simply creating a password or adding new user with password.
let me know if there is a different work around/solution