Import error when trying to access sdk datastore admin
Use from django.utils import simplejson.
dev_appserver mimics the production environment.  Nothing you install at the system level will be available for import to your scripts, to avoid imports working fine in your testing and then failing spectacularly when you deploy.  However, you don't need to bundle this particular module because it's already available in the django package installed on production (and with the SDK).
In general, you do need to include external libraries in your application directory, although you can symlink them from their installed locations and they'll generally work fine (and will be deployed to production when you deploy).
I'm getting a "ImportError: No module named simplejson" when trying to access datastore admin on the development server.
After the first time I got this error I installed the simplejson package from slackbuilds (i'm on Slackware). It seems to be working normally, I could import the simplejson module with no errors on the python console.
But the import error persists when I try to access datastore admin, even after installing the module. Restarting the development server didn't do anything.
What could be wrong?
Edit: here's the stacktrace:

Traceback (most recent call last):
  File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 3245, in _HandleRequest
      self._Dispatch(dispatcher, self.rfile, outfile, env_dict)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 3186, in _Dispatch
      base_env_dict=env_dict)   File "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 531, in Dispatch
      base_env_dict=base_env_dict)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 2410, in Dispatch
      self._module_dict)   File "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 2320, in ExecuteCGI
      reset_modules = exec_script(handler_path, cgi_path,
  hook)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 2216, in ExecuteOrImportScript
      exec module_code in script_module.dict   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/ext/datastore_admin/main.py",
  line 30, in 
      from google.appengine.ext.datastore_admin
  import copy_handler   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1945, in load_module
      return self.FindAndLoadModule(submodule,
  fullname, search_path)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1847, in FindAndLoadModule
      description)   File "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1798, in LoadModuleRestricted
      description)   File "/home/lwlun/AppEngine/google_appengine/google/appengine/ext/datastore_admin/copy_handler.py",
  line 40, in 
      from google.appengine.ext.datastore_admin
  import utils   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1945, in load_module
      return self.FindAndLoadModule(submodule,
  fullname, search_path)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1847, in FindAndLoadModule
      description)   File "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1798, in LoadModuleRestricted
      description)   File "/home/lwlun/AppEngine/google_appengine/google/appengine/ext/datastore_admin/utils.py",
  line 35, in 
      from google.appengine.ext.mapreduce import
  control   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1945, in load_module
      return self.FindAndLoadModule(submodule,
  fullname, search_path)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1847, in FindAndLoadModule
      description)   File "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1798, in LoadModuleRestricted
      description)   File "/home/lwlun/AppEngine/google_appengine/google/appengine/ext/mapreduce/control.py",
  line 26, in 
      from google.appengine.ext.mapreduce import
  handlers   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1945, in load_module
      return self.FindAndLoadModule(submodule,
  fullname, search_path)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1847, in FindAndLoadModule
      description)   File "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1295, in Decorate
      return func(self, *args, **kwargs)   File
  "/home/lwlun/AppEngine/google_appengine/google/appengine/tools/dev_appserver.py",
  line 1798, in LoadModuleRestricted
      description)   File "/home/lwlun/AppEngine/google_appengine/google/appengine/ext/mapreduce/handlers.py",
  line 26, in 
      import simplejson ImportError: No module named simplejson