def check_availability(self, isos):
<EOL>iso1name =  iso_name_converter(isos[<NUM_LIT:0>])<EOL>iso2name =  iso_name_converter(isos[<NUM_LIT:1>])<EOL>ratio = iso1name + '<STR_LIT:/>' + iso2name<EOL>ratio_inv = iso2name + '<STR_LIT:/>' + iso1name<EOL>delta = '<STR_LIT>' + iso1name + '<STR_LIT:/>' + iso2name + '<STR_LIT:)>'<EOL>delta_inv = '<STR_LIT>' + iso2name + '<STR_LIT:/>' + iso1name + '<STR_LIT:)>'<EOL>index = -<NUM_LIT:1><EOL>try:<EOL><INDENT>index = self.datadict[ratio]<EOL>delta_b = False<EOL>ratio_b = False<EOL><DEDENT>except KeyError:<EOL><INDENT>try:<EOL><INDENT>index = self.datadict[ratio_inv]<EOL>delta_b = False<EOL>ratio_b = True<EOL><DEDENT>except KeyError:<EOL><INDENT>try:<EOL><INDENT>index = self.datadict[delta]<EOL>delta_b = True<EOL>ratio_b = False<EOL><DEDENT>except KeyError:<EOL><INDENT>try:<EOL><INDENT>index = self.datadict[delta_inv]<EOL>delta_b = True<EOL>ratio_b = True<EOL><DEDENT>except KeyError:<EOL><INDENT>index = -<NUM_LIT:1><EOL>delta_b = None<EOL>ratio_b = None<EOL><DEDENT><DEDENT><DEDENT><DEDENT>return index, delta_b, ratio_b<EOL>
This routine checks if the requested set of isotopes is
available in the dataset.

Parameters
----------
isos : list
    set of isotopes in format ['Si-28','Si-30'].

Returns
-------
list
   [index, delta_b, ratio_b].
   index: where is it.
   delta_b: is it a delta value or not?
   ratio_ib:  True if ratio is inverted, false if not