code: def from_inches(value, units):
      
      lookup = {'in': lambda x: x,
                'cm': lambda x: x*2.54,
                'mm': lambda x: x*2.54*10}
      try:
          return lookup[units](value)
      except KeyError:
          raise PlotnineError("Unknown units '{}'".format(units))
docs: Convert value in inches to given units
  
      Parameters
      ----------
      value : float
          Value to be converted
      units : str
          Units to convert value to. Must be one of
          `['in', 'cm', 'mm']`.