Christopher Warner Studies and thoughts, usually in coherent fashion.

Zope2 on Python 2.5, XMP and ExifTool

Is looking promising; there is even a nice buildbot to check the progress. This is sorely needed by anyone using Plone right now, especially for me. Recently at nymag we've been implementing image management in Plone; the problem is that currently i'm using exiftool to get XMP data from a file. Sadly, this is not the best way to apporach the XMP situation for Plone Everyone Else (tm) seeing as at the very least a new python library for xmp based on Exempi is available. Caveat, only for Python 2.5. Granted, it's a C based library and ExifTool doesn't have that requirement but as far as implementation goes it's not something a unittest would need to be written for. As it stands; I still have to write unittest to accomodate ExifTool.

That aside I spent most of the last 24 hours trying to see if Plone could get rid of Exif.py. There is another tool i've been using for the last couple of weeks to do so written by Ivan Herman called xmp.py that actually finished what he started. It reads the XMP data of a freshly uploaded Plone object and applies that data to the object itself, from there it actually applies it to the file. However, this only works for gifs/jpegs and it simply won't be enough. Via standard RDF/XML and extractXMP I was able to do a return _searchXMLContent(finstance.read()) and kick the tag data back to Plone and it works well. As time is a factor it means falling back to ExifTool as the only option but I can't reliably sprint on metadata replacement until I can use a proper python library; in-fact even using the ESA's python toolkit is a stretch as it's based on a C api. My personal feelings are that Exif.py should be deprecated in favor for totally replacing that functionality with ExifTool or something else. So, in summary, ExifTool wins as the only lib with a cleanroom, no dependencies beyond perl, full-featured implementation for metadata across the board. No other lib can say this; none. In-fact, I wouldn't be surprised if anyone doing anything with Metadata for a large audience isn't using it. So it's worth the system call.

Here's a quick and dirty implementation if you are thinking about using ExifTool and Plone:

def getXMP(self, img=None, refresh=False):
"""Get XMP data from file
"""
cache = '_image_xmp'

if refresh:
setattr(self, cache, None)

xmp_data = getattr(self, cache, None)

if xmp_data is None or not isinstance(xmp_data, dict):
io = self.getImageAsFile(img, scale=None)
if io is not None:
try:
fd, fd_name = mkstemp();
stream = os.fdopen(fd, 'wb')
data = io.read()
stream.write(data)

exiftool_str = "/usr/bin/exiftool %s -CreateDate -Artist -Copyright -Creatortool -Creator -Usageterms" % fd_name
xmp_datab = Popen(exiftool_str, shell=True, stdout=subprocess.PIPE)
out = xmp_datab.stdout.read()
stream.close()
print out
#temp rename above to xmp_data and remove the below dict Chris.. this is yourself in the past telling you
# not to forget like a dumbass
xmp_data = {}
except:
LOG.error('Failed to process XMP data', exc_info=True)
xmp_data = {}
io.seek(0)

if not xmp_data:
xmp_data = {}
setattr(self, cache, xmp_data)