How do I use data in package_data from source code?

The standard pkgutil module's get_data() function will calculate the path to your data, relative to your package, and retrieve the data for you via whatever module loader Python used to import the hermes package:

import pkgutildata = pkgutil.get_data('hermes', 'templates/python.tpl')

Of course in certain cases you could just read your data using a path calculated from hermes.__file__, but if you plan to distribute your project, consider that it may be installed in different ways on the end user's machine: as plain files, deployed in a zipped egg archive, etc. In the latter case, your hermes module will have been imported by Python using a zipimporter, preventing you from doing a normal open(path).read():

>>> import hermes>>> hermes.__loader__<zipimporter object "/home/pat/.cascade/virt/foo/lib/python2.6/site-packages/foo-0.0.0-py2.6.egg">

If you're okay with adding a runtime dependency on the distribute codebase, you may want to consdider looking at the pkg_resources module, which can give you the same result but adds other capabilities.

import pkg_resourcesdata = pkg_resources.resource_string('hermes', 'templates/python.tpl')