code: def app_versions(self):
          
          if not self._app_versions:
              app_versions_url = self._build_url('versions')
  
              response = self._request('GET', app_versions_url)
  
              if response.status_code == requests.codes.not_found:
                  self._app_versions = []
              elif response.status_code == requests.codes.forbidden:
                  raise ForbiddenError(response.json()['results'][0]['detail'])
              elif response.status_code != requests.codes.ok:
                  raise APIError("Could not retrieve app versions: {}".format(response))
              else:
                  self._app_versions = response.json().get('results')
  
          return self._app_versions
docs: List of the versions of the internal KE-chain 'app' modules.