title: SQLAlchemy with pymssql slash in server name
body: <p>I am currently trying to make my connection string for SQLAlchemy to MSSQL configurable. From my testing, this works:</p>
  
  <pre><code>engine = create_engine("mssql+pymssql://username:password@dviserver\dev0000/db").connect()
  </code></pre>
  
  <p>However, how do I enter the port number into this connection string, I've tried the following and it does not work:</p>
  
  <pre><code>engine = create_engine("mssql+pymssql://username:password@dviserver\dev0000:1433/db").connect()
  </code></pre>
  
  <p>Below is the stack trace:</p>
  
  <pre><code>Traceback (most recent call last):
    File "src\pymssql.pyx", line 636, in pymssql.connect
    File "src\_mssql.pyx", line 1957, in _mssql.connect
    File "src\_mssql.pyx", line 677, in _mssql.MSSQLConnection.__init__
  _mssql.MSSQLDriverException: Connection to the database failed for an unknown reason.
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\engine\base.py", line 2158, in _wrap_pool_connect
      return fn()
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\pool.py", line 342, in unique_connection
      return _ConnectionFairy._checkout(self)
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\pool.py", line 788, in _checkout
      fairy = _ConnectionRecord.checkout(pool)
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\pool.py", line 529, in checkout
      rec = pool._do_get()
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\pool.py", line 1193, in _do_get
      self._dec_overflow()
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\util\langhelpers.py", line 66, in __exit__
      compat.reraise(exc_type, exc_value, exc_tb)
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\util\compat.py", line 249, in reraise
      raise value
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\pool.py", line 1190, in _do_get
      return self._create_connection()
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\pool.py", line 347, in _create_connection
      return _ConnectionRecord(self)
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\pool.py", line 474, in __init__
      self.__connect(first_connect_check=True)
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\pool.py", line 671, in __connect
      connection = pool._invoke_creator(self)
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\engine\strategies.py", line 106, in connect
      return dialect.connect(*cargs, **cparams)
    File "C:\conda\publisher-app\lib\site-packages\sqlalchemy\engine\default.py", line 412, in connect
      return self.dbapi.connect(*cargs, **cparams)
    File "src\pymssql.pyx", line 645, in pymssql.connect
  pymssql.InterfaceError: Connection to the database failed for an unknown reason.
  </code></pre>