How to use the pyexiv2.Rational function in pyexiv2

def string_to_rational(coordinate):
    """
    convert string to rational variable for GPS
    """

    if '.' in coordinate:
        value1, value2 = coordinate.split('.')
        return pyexiv2.Rational(int(float(value1 + value2)), 10**len(value2))
    else:
        return pyexiv2.Rational(int(coordinate), 1)

def string_to_rational(coordinate):
    """
    convert string to rational variable for GPS
    """
    if '.' in coordinate:
        value1, value2 = coordinate.split('.')
        return pyexiv2.Rational(int(float(value1 + value2)), 10**len(value2))
    else:
        return pyexiv2.Rational(int(coordinate), 1)

def string_to_rational(coordinate):
    """
    convert string to rational variable for GPS
    """

    if '.' in coordinate:
        value1, value2 = coordinate.split('.')
        return pyexiv2.Rational(int(float(value1 + value2)), 10**len(value2))
    else:
        return pyexiv2.Rational(int(coordinate), 1)

def string_to_rational(coordinate):
    """
    convert string to rational variable for GPS
    """
    if '.' in coordinate:
        value1, value2 = coordinate.split('.')
        return pyexiv2.Rational(int(float(value1 + value2)), 10**len(value2))
    else:
        return pyexiv2.Rational(int(coordinate), 1)

def string_to_rational(coordinate):
    """
    convert string to rational variable for GPS
    """
    if '.' in coordinate:
        value1, value2 = coordinate.split('.')
        return pyexiv2.Rational(int(float(value1 + value2)), 10**len(value2))
    else:
        return pyexiv2.Rational(int(coordinate), 1)

lng_deg = self.to_degree(lng, ["W", "E"])

        exiv_lat = (pyexiv2.Rational(lat_deg[0] * 60 + lat_deg[1], 60),
                    pyexiv2.Rational(lat_deg[2] * 100, 6000), pyexiv2.Rational(0, 1))
        exiv_lng = (pyexiv2.Rational(lng_deg[0] * 60 + lng_deg[1], 60),
                    pyexiv2.Rational(lng_deg[2] * 100, 6000), pyexiv2.Rational(0, 1))

        try:
            exiv_image = pyexiv2.ImageMetadata(file_name)
            exiv_image.read()

            exiv_image["Exif.GPSInfo.GPSLatitude"] = exiv_lat
            exiv_image["Exif.GPSInfo.GPSLatitudeRef"] = lat_deg[3]
            exiv_image["Exif.GPSInfo.GPSLongitude"] = exiv_lng
            exiv_image["Exif.GPSInfo.GPSLongitudeRef"] = lng_deg[3]
            exiv_image["Exif.GPSInfo.GPSAltitude"] = pyexiv2.Rational(alt, 1)
            exiv_image["Exif.GPSInfo.GPSAltitudeRef"] = '0'
            exiv_image["Exif.Image.GPSTag"] = 654
            exiv_image["Exif.GPSInfo.GPSMapDatum"] = "WGS-84"
            exiv_image["Exif.GPSInfo.GPSVersionID"] = '2 0 0 0'

            exiv_image.write(True)
        except Exception as e:
            print '[ERROR]', e

date_tag = exiv_image['Exif.Image.DateTime']

    date_max = max(date_tag.value, gps_datetime)
    date_min = min(date_tag.value, gps_datetime)
    time_diff = date_max - date_min
    if (time_diff > timedelta(seconds=5)):
        print(
            "WARNING, camera trigger and photo time different by {}".format(time_diff))
        print("  Photo tag time: {}".format(date_tag.value))
        print("  Camera trigger time: {}".format(gps_datetime))

    exiv_image["Exif.GPSInfo.GPSLatitude"] = exiv_lat
    exiv_image["Exif.GPSInfo.GPSLatitudeRef"] = lat_deg[3]
    exiv_image["Exif.GPSInfo.GPSLongitude"] = exiv_lng
    exiv_image["Exif.GPSInfo.GPSLongitudeRef"] = lng_deg[3]
    exiv_image["Exif.GPSInfo.GPSAltitude"] = pyexiv2.Rational(alt, 1)
    exiv_image["Exif.GPSInfo.GPSAltitudeRef"] = '0'
    exiv_image["Exif.Image.GPSTag"] = 654
    exiv_image["Exif.GPSInfo.GPSMapDatum"] = "WGS-84"
    exiv_image["Exif.GPSInfo.GPSVersionID"] = '2 0 0 0'

    exiv_image.write(True)