code: def get_converted(self, symbol, units='CAD', system=None, tag=None):
          
          if isinstance(symbol, (str, unicode)):
              sym = self.get(symbol)
              df = sym.df
              curu = sym.units
              requ = units
          elif isinstance(symbol, tuple):
              df = symbol[0]
              curu = symbol[1]
              requ = units
          else:
              raise TypeError("Expected str or (DataFrame, str), found {}".format(type(symbol)))
          
          system = system or self.default_system
          tag = tag or self.default_tag
          
          conv = self.converters[system][tag]
  
          newdf = conv.convert(df, curu, requ)
          newdf = pd.merge(df, newdf, left_index=True, right_index=True)
          newdf = newdf[df.columns[0] + "_y"].to_frame()
          newdf.columns = df.columns
          return newdf
docs: Uses a Symbol's Dataframe, to build a new Dataframe,
          with the data converted to the new units
          
          Parameters
          ----------
          symbol : str or tuple of the form (Dataframe, str)
              String representing a symbol's name, or a dataframe
              with the data required to be converted.  If supplying a 
              dataframe, units must be passed.
          units : str, optional
              Specify the units to convert the symbol to, default to CAD 
          system : str, optional
              If None, the default system specified at instantiation
              is used.  System defines which conversion approach to take.
          tag : str, optional
              Tags define which set of conversion data is used.  If None, the
              default tag specified at instantiation is used.