def get_octal(self, c, i):
        """Get octal."""

        index = i.index
        value = []
        zero_count = 0
        try:
            if c == '0':
                for x in range(3):
                    if c != '0':
                        break
                    value.append(c)
                    c = next(i)
            zero_count = len(value)
            if zero_count < 3:
                for x in range(3 - zero_count):
                    if c not in _OCTAL:
                        break
                    value.append(c)
                    c = next(i)
            i.rewind(1)
        except StopIteration:
            pass

        octal_count = len(value)
        if not (self.use_format and octal_count) and not (zero_count and octal_count < 3) and octal_count != 3:
            i.rewind(i.index - index)
            value = []

        return ''.join(value) if value else None
Get octal.