code: def getAllCols(self, sddsfile=None):
          
          if SDDS_:
              if sddsfile is not None:
                  sddsobj = sdds.SDDS(2)
                  sddsobj.load(sddsfile)
              else:
                  sddsobj = self.sddsobj
              return sddsobj.columnName
          else:
              if sddsfile is None:
                  sddsfile = self.sddsfile
              return subprocess.check_output(['sddsquery', '-col', sddsfile]).split()
docs: get all available column names from sddsfile
  
          :param sddsfile: sdds file name, if not given, rollback to the one that from ``__init__()``
          :return: all sdds data column names
          :rtype: list
  
          :Example:
  
          >>> dh = DataExtracter('test.out')
          >>> print(dh.getAllCols())
          ['x', 'xp', 'y', 'yp', 't', 'p', 'particleID']
          >>> print(dh.getAllCols('test.twi'))
          ['s', 'betax', 'alphax', 'psix', 'etax', 'etaxp', 'xAperture', 'betay', 'alphay', 'psiy', 'etay', 'etayp',
           'yAperture', 'pCentral0', 'ElementName', 'ElementOccurence', 'ElementType']