docs: def _initialize_client_from_environment():
      ''' Initialize a KeenClient instance using environment variables. '''
      global _client, project_id, write_key, read_key, master_key, base_url
  
      if _client is None:
          # check environment for project ID and keys
          project_id = project_id or os.environ.get("KEEN_PROJECT_ID")
          write_key = write_key or os.environ.get("KEEN_WRITE_KEY")
          read_key = read_key or os.environ.get("KEEN_READ_KEY")
          master_key = master_key or os.environ.get("KEEN_MASTER_KEY")
          base_url = base_url or os.environ.get("KEEN_BASE_URL")
  
          if not project_id:
              raise InvalidEnvironmentError("Please set the KEEN_PROJECT_ID environment variable or set keen.project_id!")
  
          _client = KeenClient(project_id,
                               write_key=write_key,
                               read_key=read_key,
                               master_key=master_key,
                               base_url=base_url)