code: def format_units(v, step=None, system="si", units=None):
      
      if v is None:
          return 0, ''
  
      for prefix, size in UnitSystems[system]:
          if condition(v, size, step):
              v2 = v / size
              if v2 - math.floor(v2) < 0.00000000001 and v > 1:
                  v2 = float(math.floor(v2))
              if units:
                  prefix = "%s%s" % (prefix, units)
              return v2, prefix
  
      if v - math.floor(v) < 0.00000000001 and v > 1:
          v = float(math.floor(v))
      if units:
          prefix = units
      else:
          prefix = ''
      return v, prefix
docs: Format the given value in standardized units.
  
      ``system`` is either 'binary' or 'si'
  
      For more info, see:
          http://en.wikipedia.org/wiki/SI_prefix
          http://en.wikipedia.org/wiki/Binary_prefix