sqlalchemy fails to connect to ms sql server

Question

Trying to connect to SQL server using SQLAlchemy with pyodbc (freeTDS) as the driver; The connections succeeds if I use pyodbc directly:

>>> import pyodbc
>>> conn = pyodbc.connect('DSN=serverdsn;UID=user;PWD=password')
>>> crsr = conn.cursor()
>>> rows = crsr.execute("select @@VERSION").fetchall()
>>> print(rows)
[('Microsoft Azure SQL Data Warehouse - 10.0.9248.28 Sep 12 2017 01:08:55 Copyright (c) Microsoft Corporation', )]
>>> crsr.close()
>>> conn.close()

But when I use SQLAlchemy, it fails with a mysterious error:

>>> from sqlalchemy import create_engine
>>> e = create_engine("mssql+pyodbc://user:password@serverdsn")
>>> with e.connect() as con:
...     rs = con.execute('select * from users')
...     for row in rs:
...         print(row)
... 

Here is the full stack trace:

Traceback (most recent call last): File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/pool.py", line 1122, in _do_get return self._pool.get(wait, self._timeout) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-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 "", line 1, in File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 2091, in connect return self._connection_cls(self, **kwargs) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 90, in init if connection is not None else engine.raw_connection() File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 2177, in raw_connection self.pool.unique_connection, _connection) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 2147, in _wrap_pool_connect return fn() File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/pool.py", line 328, in unique_connection return _ConnectionFairy._checkout(self) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/sit e-packages/sqlalchemy/pool.py", line 766, in _checkout fairy = _ConnectionRecord.checkout(pool) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/pool.py", line 516, in checkout rec = pool._do_get() File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/pool.py", line 1138, in _do_get self._dec_overflow() File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py", line 66, in exit compat.reraise(exc_type, exc_value, exc_tb) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/util/compat.py", line 187, in reraise raise value File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/pool.py", line 1135, in _do_get return self._create_connection() File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/pool.py", line 333, in _create_conne ction return _ConnectionRecord(self) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/pool.py", line 461, in init self. connect(first_connect_check=True) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/pool.py", line 661, in __connect exec_once(self.connection, self) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/event/attr.py", line 246, in exec_once self(*args, **kw) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/event/attr.py", line 256, in __call fn(*args, **kw) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py", line 1331, in go return once_fn(*arg, **kw) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/engine/strategies.py", line 181, in first_connect dialect.initialize(c) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/connectors/pyodbc.py", line 165, in initialize super(PyODBCConnector, self).initialize(co nnection) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/dialects/mssql/base.py", line 1742, in initialize super(MSDialect, self).initialize(connection) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/engine/default.py", line 256, in initialize self.get_isolation_level(connection.connection) File "/Users/purecarscomputer/anaconda/envs/tensorflow/lib/python3.5/site-packages/sqlalchemy/dialects/mssql/base.py", line 1735, in get_isolation_level "tried views: %s; final error was: %s" % (views, err)) UnboundLocalError: local variable 'err' referenced before assignment

I've tried install and uninstall sqlalchemy and searched around on google, but not find a solution. Does anyone have similar problems and have a clue about what is happening?

OS information:

ProductName:    Mac OS X
ProductVersion: 10.12.6
BuildVersion:   16G29

Answer 1

Here's the connection string I used to solve a connection problem with similar symptoms:

import urllib
from sqlalchemy import create_engine

# utilize existing odbc connection to create engine
params = urllib.quote_plus("DRIVER={}; SERVER=server; Database=database; UID=user; PWD=pw")
engine = create_engine("mssql+pyodbc:///?odbc_connect=%s" % params)

ref http://docs.sqlalchemy.org/en/latest/dialects/mssql.html#pass-through-exact-pyodbc-string