title: sqlalchemy close all connection
body: <p>I'm trying to drop my database using sqlalchemy:</p>
  <pre><code>def dropDb(self, dbName):
      self.closeConnection()
      self.selectDb(None)
      self.execute(&quot;drop database %s&quot; % dbName)
  
  def closeConnection(self):
      self._Session.close_all()
      self._engine.dispose()
      del self._Session
      del self._engine
  </code></pre>
  <p>I create the engine with:</p>
  <pre><code>sqlalchemy.create_engine(connection_string, poolclass = NullPool)
  </code></pre>
  <p>But I am getting the following error:</p>
  <blockquote>
  <p>Detail ProgrammingError: (ProgrammingError) ('42000', '[42000]
  [Microsoft][ODBC SQL Server Driver][SQL Server]Cannot drop database
  &quot;test_db&quot; because it is currently in use. (3702) (SQLExecDirectW)')
  'drop database test_db' ()</p>
  </blockquote>
  <p>How can I forcibly close ALL connections?</p>