code: def connect(db_url=None,
              pooling=hgvs.global_config.uta.pooling,
              application_name=None,
              mode=None,
              cache=None):
      
  
      _logger.debug('connecting to ' + str(db_url) + '...')
  
      if db_url is None:
          db_url = _get_ncbi_db_url()
  
      url = _parse_url(db_url)
      if url.scheme == 'postgresql':
          conn = NCBI_postgresql(
              url=url, pooling=pooling, application_name=application_name, mode=mode, cache=cache)
      else:
          # fell through connection scheme cases
          raise RuntimeError("{url.scheme} in {url} is not currently supported".format(url=url))
      _logger.info('connected to ' + str(db_url) + '...')
      return conn
docs: Connect to a uta/ncbi database instance.
  
      :param db_url: URL for database connection
      :type db_url: string
      :param pooling: whether to use connection pooling (postgresql only)
      :type pooling: bool
      :param application_name: log application name in connection (useful for debugging; PostgreSQL only)
      :type application_name: str
  
      When called with an explicit db_url argument, that db_url is used for connecting.
  
      When called without an explicit argument, the function default is
      determined by the environment variable UTA_DB_URL if it exists, or
      hgvs.datainterface.uta.public_db_url otherwise.
  
      >>> hdp = connect()
      >>> hdp.schema_version()
      '1.1'
  
      The format of the db_url is driver://user:pass@host/database (the same
      as that used by SQLAlchemy).  Examples:
  
      A remote public postgresql database:
          postgresql://anonymous:anonymous@uta.biocommons.org/uta'
  
      A local postgresql database:
          postgresql://localhost/uta
  
      A local SQLite database:
        sqlite:////tmp/uta-0.0.6.db
  
      For postgresql db_urls, pooling=True causes connect to use a
      psycopg2.pool.ThreadedConnectionPool.