def _format_value_error(self, v, e, pm="<STR_LIT>"):
<EOL>if not _s.fun.is_a_number(v) or not _s.fun.is_a_number(e)or v in [_n.inf, _n.nan, _n.NAN] or e in [_n.inf, _n.nan, _n.NAN]: <EOL><INDENT>return str(v)+pm+str(e)<EOL><DEDENT>try:<EOL><INDENT>sig_figs = -int(_n.floor(_n.log10(abs(e))))+<NUM_LIT:1>            <EOL>return str(_n.round(v, sig_figs)) + pm + str(_n.round(e, sig_figs))<EOL><DEDENT>except:<EOL><INDENT>return str(v)+pm+str(e)<EOL><DEDENT>
Returns a string v +/- e with the right number of sig figs.