code: def set_root_login(self, r):
          
  
          # Check the legacy password location.
          try:
              r.env.db_root_username = r.env.root_username
          except AttributeError:
              pass
          try:
              r.env.db_root_password = r.env.root_password
          except AttributeError:
              pass
  
          # Check the new password location.
          key = r.env.get('db_host')
          if self.verbose:
              print('db.set_root_login.key:', key)
              print('db.set_root_logins:', r.env.root_logins)
          if key in r.env.root_logins:
              data = r.env.root_logins[key]
  #             print('data:', data)
              if 'username' in data:
                  r.env.db_root_username = data['username']
                  r.genv.db_root_username = data['username']
              if 'password' in data:
                  r.env.db_root_password = data['password']
                  r.genv.db_root_password = data['password']
          else:
              msg = 'Warning: No root login entry found for host %s in role %s.' % (r.env.get('db_host'), self.genv.get('ROLE'))
              print(msg, file=sys.stderr)
docs: Looks up the root login for the given database on the given host and sets
          it to environment variables.
  
          Populates these standard variables:
  
              db_root_password
              db_root_username