def delta_to_ratio(self, isos_ss, delta, 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>ratio = (old_div(delta, <NUM_LIT>) + <NUM_LIT:1>) * ss_ratio<EOL>if oneover:<EOL><INDENT>ratio = old_div(<NUM_LIT:1>,ratio)<EOL><DEDENT>return ratio<EOL>
Transforms a delta value into an isotopic ratio

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

Returns
-------
float
    delta value