def ratio_to_delta(self, isos_ss, ratio, oneover=False):
<EOL>if type(isos_ss) == float:<EOL><INDENT>ss_ratio = isos_ss<EOL><DEDENT>elif type(isos_ss) == list:<EOL><INDENT>ss_ratio = self.inut.isoratio_init(isos_ss)<EOL><DEDENT>else:<EOL><INDENT>print('<STR_LIT>')<EOL>return None<EOL><DEDENT>if oneover:<EOL><INDENT>ratio = old_div(<NUM_LIT:1>,ratio)<EOL><DEDENT>delta = (old_div(ratio, ss_ratio) - <NUM_LIT:1.>) * <NUM_LIT><EOL>return delta<EOL>
Transforms an isotope ratio into a delta value

Parameters
----------
isos_ss: list or float
    list w/ isotopes, e.g., ['N-14','N-15'] OR the solar
    system ratio.
ratio : float
    ratio of the isotopes to transform.
oneover : boolean
    take the inverse of the ratio before transforming (never
    inverse of delta value!).  The default is False.

Returns
-------
float
    delta value