[#4801] Selective loading in plugins toolkit

This took a while to get right because exceptions raised during the
toolkit initialization fail silently and the sympton would be the an
import error later on when trying to import something from the toolkit:

from ckan.plugins.toolkit import get_action

ImportError: cannot import name 'get_action'

TODO: Sort out what gets exposed to extensions in terms of CLI commands

ckan/plugins/toolkit.py

@@ -130,14 +130,14 @@ def __init__(self):
     def _initialize(self):
         ''' get the required functions/objects, store them for later
         access and check that they match the contents dict. '''
-
+        import six
         import ckan
-        import ckan.lib.base as base
         import ckan.logic as logic
+
+        import ckan.lib.base as base
         import ckan.logic.validators as logic_validators
         import ckan.lib.navl.dictization_functions as dictization_functions
         import ckan.lib.helpers as h
-        import ckan.lib.cli as cli
         import ckan.lib.plugins as lib_plugins
         import ckan.common as common
         from ckan.exceptions import (
@@ -147,8 +147,10 @@ def _initialize(self):
         from ckan.lib.jobs import enqueue as enqueue_job
 
         import ckan.common as converters
-        import pylons
-        import webhelpers.html.tags
+        if six.PY2:
+            import ckan.lib.cli as cli
+            import pylons
+            import webhelpers.html.tags
 
         # Allow class access to these modules
         self.__class__.ckan = ckan
@@ -213,6 +215,7 @@ def _initialize(self):
 
 '''
         t['render'] = base.render
+        t['abort'] = base.abort
         t['asbool'] = converters.asbool
         self.docstring_overrides['asbool'] = '''Convert a string (e.g. 1,
 true, True) from the config file into a boolean.
@@ -234,7 +237,6 @@ def _initialize(self):
 For example: ``bar = toolkit.aslist(config.get('ckan.foo.bar', []))``
 
 '''
-        t['literal'] = webhelpers.html.tags.literal
 
         t['get_action'] = logic.get_action
         t['chained_action'] = logic.chained_action
@@ -251,22 +253,10 @@ def _initialize(self):
         t['UnknownValidator'] = logic.UnknownValidator
         t['Invalid'] = logic_validators.Invalid
 
-        t['CkanCommand'] = cli.CkanCommand
-        t['load_config'] = cli.load_config
         t['DefaultDatasetForm'] = lib_plugins.DefaultDatasetForm
         t['DefaultGroupForm'] = lib_plugins.DefaultGroupForm
         t['DefaultOrganizationForm'] = lib_plugins.DefaultOrganizationForm
 
-        t['response'] = pylons.response
-        self.docstring_overrides['response'] = '''The Pylons response object.
-
-Pylons uses this object to generate the HTTP response it returns to the web
-browser. It has attributes like the HTTP status code, the response headers,
-content type, cookies, etc.
-
-'''
-        t['BaseController'] = base.BaseController
-        t['abort'] = base.abort
         t['redirect_to'] = h.redirect_to
         t['url_for'] = h.url_for
         t['get_or_bust'] = logic.get_or_bust
@@ -290,6 +280,22 @@ def _initialize(self):
         t['HelperError'] = HelperError
         t['enqueue_job'] = enqueue_job
 
+        if six.PY2:
+
+            t['literal'] = webhelpers.html.tags.literal
+            t['response'] = pylons.response
+            self.docstring_overrides['response'] = '''The Pylons response object.
+
+Pylons uses this object to generate the HTTP response it returns to the web
+browser. It has attributes like the HTTP status code, the response headers,
+content type, cookies, etc.
+
+'''
+            t['BaseController'] = base.BaseController
+            # TODO: Sort these out
+            t['CkanCommand'] = cli.CkanCommand
+            t['load_config'] = cli.load_config
+
         # check contents list correct
         errors = set(t).symmetric_difference(set(self.contents))
         if errors: