Declare namespace package with pkgutil module.

Use the builtin module instead of pkg_resources from setuptools.
This is compatible with PEP 420 namespace packages in Python 3.

Author: pavoljuhas

setup.py

@@ -73,8 +73,7 @@ def getversioncfg():
 setup_args = dict(
     name = "diffpy.srfit",
     version = versiondata.get('DEFAULT', 'version'),
-    namespace_packages = ['diffpy'],
-    packages = find_packages('src'),
+    packages = find_packages(os.path.join(MYDIR, 'src')),
     package_dir = {'' : 'src'},
     test_suite = 'diffpy.srfit.tests',
     include_package_data = True,

src/diffpy/__init__.py

@@ -16,10 +16,12 @@
 
 """diffpy - tools for structure analysis by diffraction.
 
-This is the namespace package shared by all DiffPy software.
+Blank namespace package.
 """
 
-__import__('pkg_resources').declare_namespace(__name__)
+
+from pkgutil import extend_path
+__path__ = extend_path(__path__, __name__)
 
 
 # End of file