docs: def parse_eff(filename):
      """
      Parse through Jean-Marcs OSSSO .eff files.
      
      The efficiency files comes in 'chunks' meant to be used at different 'rates' of motion.
  
      """
      blocks = []
      block = {}
  
      with open(filename) as efile:
          for line in efile.readlines():
              if line.lstrip().startswith("#"):
                  continue
              keyword = line.lstrip().split("=")[0]
              funcs = {'square_param': parse_square_param, 
                       'rates': rates}
              block[keyword] = funcs.get(keyword, dummy)(line)
              if keyword == 'mag_lim':
                  blocks.append(block)
                  block = {}
  
      return blocks