def frequencies(self, sides=None):
<EOL>if sides is None:<EOL><INDENT>sides = self.sides<EOL><DEDENT>if sides not in self._sides_choices:<EOL><INDENT>raise errors.SpectrumChoiceError(sides, self._sides_choices)<EOL><DEDENT>if sides == '<STR_LIT>':<EOL><INDENT>return self._range.onesided()<EOL><DEDENT>if sides == '<STR_LIT>':<EOL><INDENT>return self._range.twosided()<EOL><DEDENT>if sides == '<STR_LIT>':<EOL><INDENT>return self._range.centerdc()<EOL><DEDENT>
Return the frequency vector according to :attr:`sides`