code: def logout(lancet, service):
      
      if service:
          services = [service]
      else:
          services = ['tracker', 'harvest']
  
      for service in services:
          url = lancet.config.get(service, 'url')
          key = 'lancet+{}'.format(url)
          username = lancet.config.get(service, 'username')
          with taskstatus('Logging out from {}', url) as ts:
              if keyring.get_password(key, username):
                  keyring.delete_password(key, username)
                  ts.ok('Logged out from {}', url)
              else:
                  ts.ok('Already logged out from {}', url)
docs: Forget saved passwords for the web services.