In [1]: from libxmp import XMPFiles, XMPMeta, consts

 In [2]: xmpfile = XMPFiles(file_path='XMPSpecificationPart1.pdf', openforupdate=True)

 In [3]: myxmp = xmpfile.get_xmp()

 In [4]: print myxmp.get_localized_text(consts.XMP_NS_DC, 'title', '', 'x-default')
         XMP Specification Part 1: Data Model, Serialization, and Core Properties

 In [5]: myxmp.set_property(consts.XMP_NS_DC, 'title[1]/?xml:lang', 'en')

 In [6]: myxmp.set_localized_text(consts.XMP_NS_DC, 'title', '', 'de', 'XMP-Spezifikation, Teil 1')

 In [7]: print myxmp.get_property(consts.XMP_NS_XMP, 'MetadataDate')
         2012-03-21T08:57:17-07:00

 In [8]: import datetime
         jetzt = datetime.datetime.now().strftime("%Y-%m-%dT%H:%M:%S+01:00")

 In [9]: myxmp.set_property(consts.XMP_NS_XMP, 'MetadataDate', jetzt)

 In [10]: print myxmp.get_property(consts.XMP_NS_XMP, 'MetadataDate')
          2016-02-21T19:33:26+01:00

 In [11]: xmpfile.can_put_xmp(myxmp)
          True