an example of how to set some exif data on an image.

set_exif.py

#!/usr/bin/python
from gi.repository import GExiv2
import pprint

exif = GExiv2.Metadata('test.jpg')
lat = exif.get_gps_latitude()
lon = exif.get_gps_longitude()

print "Latitude: %s" % lat
print "Longitude: %s" % lon

# longitude, latitude, altitude
exif.set_gps_info(-41.3969702721, 122.6295057244, 76)

# Using dict notation like this reads/writes RAW string values
# into the EXIF data, with no modification/interpolation by GExiv2.
# Refer to GExiv2.py to see what kind of convenience methods are
# supplied for setting/getting non-string values.
IPTC = 'Iptc.Application2.'
exif[IPTC + 'City'] = 'Vatican City'
exif[IPTC + 'ProvinceState'] = 'The Vatican'
exif[IPTC + 'CountryName'] = 'The Vatican'
exif.save_file()