title: SQLAlchemy can't connect to Oracle database using database URL
body: <p>I am trying to create a Docker container that connects to a VPN and then checks that it can connect to some databases. Currently I'm using the following code:</p>
  
  <pre><code>DB_URI_PREFIX = {
      'mssql': 'mssql+pymssql://', 'oracle': 'oracle+cx_oracle://', 'postgres': 'postgres://',
  }
  
  
  def connect_to_db(db_type: str, host: str, username: str, password: str, database: str):
      db_uri = '{}{}:{}@{}/{}'.format(DB_URI_PREFIX[db_type], username, password, host, database)
      engine = create_engine(db_uri)
      connection = engine.connect()
      print('Successfully connected to {}/{}'.format(host, database))
      connection.close()
  </code></pre>
  
  <p><code>db_uri</code> in this case ends up being <code>mssql+pymssql://user:pass@host:port_num/database_name</code> for an SQL Server database and <code>oracle+cx_oracle://user:pass@host:port_num/database_name</code> for an Oracle database.</p>
  
  <p>The above works fine for the SQL server and Postgres databases but for the Oracle one I get this error:</p>
  
  <pre><code> Traceback (most recent call last):
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 2158, in _wrap_pool_connect
      return fn()
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 345, in unique_connection
      return _ConnectionFairy._checkout(self)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 782, in _checkout
      fairy = _ConnectionRecord.checkout(pool)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 532, in checkout
      rec = pool._do_get()
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 1186, in _do_get
      self._dec_overflow()
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/util/langhelpers.py", line 66, in __exit__
      compat.reraise(exc_type, exc_value, exc_tb)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/util/compat.py", line 187, in reraise
      raise value
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 1183, in _do_get
      return self._create_connection()
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 350, in _create_connection
      return _ConnectionRecord(self)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 477, in __init__
      self.__connect(first_connect_check=True)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 667, in __connect
      connection = pool._invoke_creator(self)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/strategies.py", line 105, in connect
      return dialect.connect(*cargs, **cparams)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/default.py", line 410, in connect
      return self.dbapi.connect(*cargs, **cparams)
  cx_Oracle.DatabaseError: ORA-12545: Connect failed because target host or object does not exist
  
  The above exception was the direct cause of the following exception:
  
  Traceback (most recent call last):
    File "connect_to_db.py", line 37, in &lt;module&gt;
      connect_to_db(args.db_type, args.host, args.username, args.password, args.database)
    File "connect_to_db.py", line 16, in connect_to_db
      connection = engine.connect()
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 2102, in connect
      return self._connection_cls(self, **kwargs)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 90, in __init__
      if connection is not None else engine.raw_connection()
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 2188, in raw_connection
      self.pool.unique_connection, _connection)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 2162, in _wrap_pool_connect
      e, dialect, self)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 1476, in _handle_dbapi_exception_noconnection
      exc_info
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause
      reraise(type(exception), exception, tb=exc_tb, cause=cause)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/util/compat.py", line 186, in reraise
      raise value.with_traceback(tb)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 2158, in _wrap_pool_connect
      return fn()
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 345, in unique_connection
      return _ConnectionFairy._checkout(self)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 782, in _checkout
      fairy = _ConnectionRecord.checkout(pool)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 532, in checkout
      rec = pool._do_get()
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 1186, in _do_get
      self._dec_overflow()
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/util/langhelpers.py", line 66, in __exit__
      compat.reraise(exc_type, exc_value, exc_tb)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/util/compat.py", line 187, in reraise
      raise value
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 1183, in _do_get
      return self._create_connection()
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 350, in _create_connection
      return _ConnectionRecord(self)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 477, in __init__
      self.__connect(first_connect_check=True)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/pool.py", line 667, in __connect
      connection = pool._invoke_creator(self)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/strategies.py", line 105, in connect
      return dialect.connect(*cargs, **cparams)
    File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/default.py", line 410, in connect
      return self.dbapi.connect(*cargs, **cparams)
  sqlalchemy.exc.DatabaseError: (cx_Oracle.DatabaseError) ORA-12545: Connect failed because target host or object does not exist (Background on this error at: http://sqlalche.me/e/4xp6)
  </code></pre>
  
  <p>Initially I thought this meant that the host could not be found but it responds when pinging it. Also, bizarrely, if I connect using cx_Oracle directly with an 'Oracle style' connection string and give that to SQLAlchemy, I can connect:</p>
  
  <pre><code>def get_oracle_connection(conn_str: str):
      return cx_Oracle.connect(conn_str)
  
  
  def connect_to_db(host: str, username: str, password: str, database: str):
      conn_str = '{}/{}@{}/{}'.format(username, password, host, database)
      conn_creator = partial(get_oracle_connection, conn_str=conn_str)
      engine = create_engine('oracle+cx_oracle://', creator=conn_creator)
  
      connection = engine.connect()
      print('Successfully connected to {}'.format(conn_str))
      connection.close()
  </code></pre>
  
  <p>In this case <code>conn_str</code> would be <code>user/pass@host/database_name</code>.</p>
  
  <p>In my Docker container I'm running Python 3 and connecting to the VPN using openconnect. I have also installed the Oracle instantclient in my container.</p>
  
  <p>requirements.txt:</p>
  
  <pre><code>SQLAlchemy==1.2.2
  pymssql==2.1.3
  cx-Oracle==6.1
  psycopg2==2.7.4
  </code></pre>
  
  <p>Am I making a mistake somewhere here or is this a bug with SQLAlchemy?</p>