code: def _determine_default_project(project=None):
      
      if project is None:
          project = _get_gcd_project()
  
      if project is None:
          project = _base_default_project(project=project)
  
      return project
docs: Determine default project explicitly or implicitly as fall-back.
  
      In implicit case, supports four environments. In order of precedence, the
      implicit environments are:
  
      * DATASTORE_DATASET environment variable (for ``gcd`` / emulator testing)
      * GOOGLE_CLOUD_PROJECT environment variable
      * Google App Engine application ID
      * Google Compute Engine project ID (from metadata server)
  
      :type project: str
      :param project: Optional. The project to use as default.
  
      :rtype: str or ``NoneType``
      :returns: Default project if it can be determined.