diff --git a/.gitignore b/.gitignore
index 5503138..162c415 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@
 /build
 /dist
 /.coverage
+.kitchen
diff --git a/.kitchen-verify.sh b/.kitchen-verify.sh
new file mode 100755
index 0000000..fb3adde
--- /dev/null
+++ b/.kitchen-verify.sh
@@ -0,0 +1,22 @@
+#!/bin/bash
+#set -x
+
+# setup
+source /*.env
+INVENTORY_BASE_URI=/tmp/kitchen/test/model/$MODEL
+RECLASS=/tmp/kitchen
+
+# prereq
+python -m ensurepip --default-pip
+pip install pipenv
+
+# env
+cd $RECLASS
+pipenv --venv || pipenv install --python ${PYVER}
+test -e /etc/reclsss || mkdir /etc/reclass
+cp -avf $INVENTORY_BASE_URI/reclass-config* /etc/reclass
+
+# verify
+for n in $(ls $INVENTORY_BASE_URI/nodes/*|sort); do
+  pipenv run python${PYVER} ./reclass.py --inventory-base-uri=$INVENTORY_BASE_URI --nodeinfo $(basename $n .yml)
+done
diff --git a/.kitchen.yml b/.kitchen.yml
new file mode 100644
index 0000000..45be629
--- /dev/null
+++ b/.kitchen.yml
@@ -0,0 +1,41 @@
+---
+driver:
+  name: docker
+  priviledged: false
+  use_sudo: false
+  volume:
+    - <%= ENV['PWD'] %>:/tmp/kitchen
+
+
+provisioner:
+  name: shell
+  script: .kitchen-verify.sh
+
+
+verifier:
+  name: inspec
+
+<%- pyver = ENV['PYTHON_VERSION'] || '2.7' %>
+
+platforms:
+  <% `find test/model -maxdepth 1 -mindepth 1 -type d |sort -u`.split().each do |model| %>
+  <% model=model.split('/')[2] %>
+  - name: <%= model %>
+    driver_config:
+      image: python:<%= pyver %>
+      platform: ubuntu
+      hostname: reclass
+      provision_command:
+        #FIXME, setup reclass env (prereq, configs, upload models)
+        #- apt-get install -y rsync
+        - echo "
+            export LC_ALL=C.UTF-8;\n
+            export LANG=C.UTF-8;\n
+            export PYVER=<%= pyver %>;\n
+            export MODEL=<%= model %>;\n
+          " > /kitchen.env
+  <% end %>
+
+suites:
+  - name: model
+
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..b060639
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,116 @@
+sudo: required
+language: python
+dist: trusty
+cache: pip
+python:
+- '2.7'
+- '3.6'
+service:
+- docker
+
+#apt:
+  #update: true
+
+#stages:
+#- name: test
+#- name: coverage
+#- name: models
+#- name: build
+#  if: fork = false
+#- name: publish
+#  if: tag =~ ^v.* and fork = false and branch = 'master'
+
+env:
+  global:
+    - PACKAGENAME="reclass"
+
+install: &pyinst
+- pip install pyparsing
+- pip install PyYAML
+# To test example models with kitchen:
+- |
+  test -e Gemfile || cat <<EOF > Gemfile
+  source 'https://rubygems.org'
+  gem 'rake'
+  gem 'test-kitchen'
+  gem 'kitchen-docker'
+  gem 'kitchen-inspec'
+  gem 'inspec'
+- bundle install
+
+script:
+- python setup.py install
+- find . reclass -name 'test_*.py' | sort | xargs -n1 -i% bash -c "echo %; python %"
+# To test example models with kitchen:
+- export PYTHON_VERSION=$TRAVIS_PYTHON_VERSION
+- kitchen list
+- kitchen test
+
+# NOTE: travis stage builds, below saved for future reference
+#jobs:
+#  include:
+#  - stage: test
+#    script: &unittest
+#    - python setup.py install
+#    - find . reclass -name 'test_*.py' | sort | xargs -n1 -i% bash -c "echo %; python %"
+#
+#  - stage: coverage
+#    install: *pyinst
+#    script:
+#    - python3 -m pytest --cov=. --cov-report=term-missing:skip-covered
+#    - coverage xml
+#    #- coveralls
+#    #- |
+#        #[ ! -z "${CODACY_PROJECT_TOKEN}" ] && python-codacy-coverage -r coverage.xml || echo "Codacy coverage NOT exported"
+#
+#  - stage: lint
+#    script:
+#    - python3 -m flake8
+#
+#  - stage: models
+#    install: &kitchen
+#    - pip install PyYAML
+#    - pip install virtualenv
+#    - |
+#      test -e Gemfile || cat <<EOF > Gemfile
+#      source 'https://rubygems.org'
+#      gem 'rake'
+#      gem 'test-kitchen'
+#      gem 'kitchen-docker'
+#      gem 'kitchen-inspec'
+#      gem 'inspec'
+#    - bundle install
+#    script:
+#    - export PYTHON_VERSION=$TRAVIS_PYTHON_VERSION
+#    - kitchen list
+#    #FIXME- kitchen test
+#
+#  - stage: build
+#    install: *pyinst
+#    script: []
+#
+#  - stage: publish
+#    install:
+#    - "/bin/true"
+#    script:
+#    - "/bin/true"
+#    deploy:
+#      provider: pypi
+#      user: epcim
+#      password:
+#        secure: TBD
+#      on:
+#        tags: true
+#        repo: salt-formulas/reclass
+#        branch: master
+#        #FIXME, $TRAVIS_PYTHON_VERSION == '2.7'
+
+notifications:
+  webhooks:
+    on_success: change  # options: [always|never|change] default: always
+    on_failure: never
+    on_start: never
+    on_cancel: never
+    on_error: never
+  email: true
+
diff --git a/Pipfile b/Pipfile
new file mode 100644
index 0000000..525e7cc
--- /dev/null
+++ b/Pipfile
@@ -0,0 +1,17 @@
+[[source]]
+url = "https://pypi.python.org/simple"
+verify_ssl = true
+name = "pypi"
+
+[dev-packages]
+
+[packages]
+pyparsing = "*"
+PyYAML = "*"
+six = "*"
+pyyaml = "*"
+# FIXME, issues with compile phase
+#"pygit2" = "*"
+
+[requires]
+python_version = "2.7"
diff --git a/README-extentions.rst b/README-extentions.rst
index b443d01..a18a37a 100644
--- a/README-extentions.rst
+++ b/README-extentions.rst
@@ -208,7 +208,6 @@
   group_errors: True
 
 
-
 Use global classes
 ------------------
 
@@ -231,6 +230,82 @@
   global_class_regexp = ['.*global']
 
 
+Use references in class names
+-----------------------------
+
+Allows to use references in the class names.
+
+References pointed to in class names cannot themselves reference another key, they should be simple strings.
+
+To avoid pitfalls do not over-engineer your class references. They should be used only for core conditions and only for them.
+A short example: `- system.wrodpress.db.${_class:database_backend}`.
+
+Best practices:
+- use references in class names always load your global class specification prior the reference is used.
+- structure your class references under parameters under one key (for example `_class`).
+- use class references as a kind of "context" or "global" available options you always know what they are set.
+
+Class referencing for existing reclass users. Frequently when constructing your models you had to load or not load some
+classes based on your setup. In most cases this lead to fork of a model or introducing kind of template generator (like cookiecutter) to
+create a model based on the base "context" or "global" variables. Class referencing is a simple way how to avoid
+"pre-processors" like this and if/else conditions around class section.
+
+
+Assuming following class setup:
+
+* node is loading `third.yml` class only
+
+
+Classes:
+
+.. code-block:: yaml
+  #/etc/reclass/classes/global.yml
+  parameters:
+    _class:
+      env:
+        override: 'env.dev'
+    lab:
+      name: default
+
+  #/etc/reclass/classes/lab/env/dev.yml
+  parameters:
+    lab:
+      name: dev
+
+  #/etc/reclass/classes/second.yml
+  classes:
+    - global
+    - lab.${_class:env:override}
+
+  #/etc/reclass/classes/third.yml
+  classes:
+    - global
+    - second
+
+
+Reclass --nodeinfo then returns:
+
+.. code-block:: yaml
+
+  ...
+  ...
+  applications: []
+  environment: base
+  exports: {}
+  classes:
+  - global
+  - lab.${_class:env:override}
+  - second
+  parameters:
+    _class:
+      env:
+        override: env.dev
+    lab:
+      name: dev
+    ...
+    ...
+
+
 Inventory Queries
 -----------------
 
diff --git a/README.rst b/README.rst
index 99de5f6..b865e4f 100644
--- a/README.rst
+++ b/README.rst
@@ -24,3 +24,26 @@
 
 Documentation covering the original version is in the doc directory.
 See the README-extensions.rst file for documentation on the extentions.
+
+
+
+Reclass related projects/tools
+==============================
+
+Queries:
+
+* yg, yaml grep with 'jq' syntax - https://gist.github.com/epcim/f1c5b748fa7c942de50677aef04f29f8, (https://asciinema.org/a/84173)
+* reclass-graph - https://github.com/tomkukral/reclass-graph
+  
+Introspection, manupulation:
+
+* reclass-tools, for manipulating reclass models - https://github.com/dis-xcom/reclass_tools
+
+YAML merge tools:
+
+* spruce, general purpose YAML & JSON merging tool - https://github.com/geofffranks/spruce
+
+Other:
+
+* saltclass, new pillar/master_tops module for salt with the behaviour of reclass - https://github.com/saltstack/salt/pull/42349
+
diff --git a/reclass.py b/reclass.py
index a0d8eb8..9c71a10 100755
--- a/reclass.py
+++ b/reclass.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–13 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import reclass.cli
 reclass.cli.main()
diff --git a/reclass/__init__.py b/reclass/__init__.py
index a79c8e1..3739b5e 100644
--- a/reclass/__init__.py
+++ b/reclass/__init__.py
@@ -6,11 +6,14 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
-from reclass.output import OutputLoader
-from reclass.storage.loader import StorageBackendLoader
-from reclass.storage.memcache_proxy import MemcacheProxy
-
+from .output import OutputLoader
+from .storage.loader import StorageBackendLoader
+from .storage.memcache_proxy import MemcacheProxy
 
 def get_storage(storage_type, nodes_uri, classes_uri, **kwargs):
     storage_class = StorageBackendLoader(storage_type).load()
diff --git a/reclass/adapters/__init__.py b/reclass/adapters/__init__.py
index 8a17572..06edb64 100755
--- a/reclass/adapters/__init__.py
+++ b/reclass/adapters/__init__.py
@@ -5,4 +5,8 @@
 #
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
-#
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
diff --git a/reclass/adapters/ansible.py b/reclass/adapters/ansible.py
index f6e9af3..abf7df2 100755
--- a/reclass/adapters/ansible.py
+++ b/reclass/adapters/ansible.py
@@ -14,6 +14,11 @@
 # The ansible adapter has received little testing and may not work at all now.
 
 
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 import os, sys, posix, optparse
 
 from six import iteritems
@@ -89,9 +94,9 @@
 
             data = groups
 
-        print output(data, options.output, options.pretty_print, options.no_refs)
+        print(output(data, options.output, options.pretty_print, options.no_refs))
 
-    except ReclassException, e:
+    except ReclassException as e:
         e.exit_with_message(sys.stderr)
 
     sys.exit(posix.EX_OK)
diff --git a/reclass/adapters/salt.py b/reclass/adapters/salt.py
index 31179ff..ce4e792 100755
--- a/reclass/adapters/salt.py
+++ b/reclass/adapters/salt.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import os, sys, posix
 
@@ -122,9 +126,9 @@
                        class_mappings=class_mappings,
                        **defaults)
 
-        print output(data, options.output, options.pretty_print, options.no_refs)
+        print(output(data, options.output, options.pretty_print, options.no_refs))
 
-    except ReclassException, e:
+    except ReclassException as e:
         e.exit_with_message(sys.stderr)
 
     sys.exit(posix.EX_OK)
diff --git a/reclass/cli.py b/reclass/cli.py
index d1b22b8..44694c5 100644
--- a/reclass/cli.py
+++ b/reclass/cli.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import sys, os, posix
 
@@ -38,9 +42,9 @@
         else:
             data = reclass.inventory()
 
-        print output(data, options.output, options.pretty_print, options.no_refs)
+        print(output(data, options.output, options.pretty_print, options.no_refs))
 
-    except ReclassException, e:
+    except ReclassException as e:
         e.exit_with_message(sys.stderr)
 
     sys.exit(posix.EX_OK)
diff --git a/reclass/config.py b/reclass/config.py
index e9bb43b..1a6ba81 100644
--- a/reclass/config.py
+++ b/reclass/config.py
@@ -6,13 +6,17 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import yaml, os, optparse, posix, sys
 
-import errors
-from defaults import *
-from constants import MODE_NODEINFO, MODE_INVENTORY
-from reclass import get_path_mangler
+from . import errors, get_path_mangler
+from .defaults import *
+from .constants import MODE_NODEINFO, MODE_INVENTORY
+
 
 def make_db_options_group(parser, defaults={}):
     ret = optparse.OptionGroup(parser, 'Database options',
@@ -171,7 +175,7 @@
 
 
 def vvv(msg):
-    #print >>sys.stderr, msg
+    #print(msg, file=sys.stderr)
     pass
 
 
@@ -180,8 +184,8 @@
     for d in dirs:
         f = os.path.join(d, filename)
         if os.access(f, os.R_OK):
-            vvv('Using config file: {0}'.format(f))
-            return yaml.safe_load(file(f))
+            vvv('Using config file: {0}'.format(str(f)))
+            return yaml.safe_load(open(f))
         elif os.path.isfile(f):
             raise PermissionsError('cannot read %s' % f)
     return {}
diff --git a/reclass/constants.py b/reclass/constants.py
index f69fa8c..58f7769 100644
--- a/reclass/constants.py
+++ b/reclass/constants.py
@@ -6,6 +6,11 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 
 class _Constant(object):
 
diff --git a/reclass/core.py b/reclass/core.py
index 3dcacac..a90b9be 100644
--- a/reclass/core.py
+++ b/reclass/core.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import copy
 import time
@@ -21,16 +25,14 @@
 from reclass.settings import Settings
 from reclass.output.yaml_outputter import ExplicitDumper
 from reclass.datatypes import Entity, Classes, Parameters, Exports
-from reclass.errors import MappingFormatError, ClassNotFound, InvQueryClassNotFound, InvQueryError, InterpolationError
+from reclass.errors import MappingFormatError, ClassNameResolveError, ClassNotFound, InvQueryClassNameResolveError, InvQueryClassNotFound, InvQueryError, InterpolationError, ResolveError
 from reclass.values.parser import Parser
 
-try:
-    basestring
-except NameError:
-    basestring = str
 
 class Core(object):
 
+    _parser = Parser()
+
     def __init__(self, storage, class_mappings, settings, input_data=None):
         self._storage = storage
         self._class_mappings = class_mappings
@@ -99,7 +101,7 @@
         p = Parameters(self._input_data, self._settings)
         return Entity(self._settings, parameters=p, name='input data')
 
-    def _recurse_entity(self, entity, merge_base=None, seen=None, nodename=None, environment=None):
+    def _recurse_entity(self, entity, merge_base=None, context=None, seen=None, nodename=None, environment=None):
 
         # values/parser in order to interpolate references in classes
         _parser = Parser()
@@ -113,9 +115,22 @@
         if merge_base is None:
             merge_base = Entity(self._settings, name='empty (@{0})'.format(nodename))
 
+        if context is None:
+            context = Entity(self._settings, name='empty (@{0})'.format(nodename))
+
         for klass in entity.classes.as_list():
-            if merge_base is not None:
-               klass=str(_parser.parse(klass, self._settings).render(merge_base.parameters.as_dict(), {}))
+
+            #if merge_base is not None:
+            #   klass=str(_parser.parse(klass, self._settings).render(merge_base.parameters.as_dict(), {}))
+            
+            if klass.count('$') > 0:
+                try:
+                    klass = str(self._parser.parse(klass, self._settings).render(merge_base.parameters.as_dict(), {}))
+                except ResolveError as e:
+                    try:
+                        klass = str(self._parser.parse(klass, self._settings).render(context.parameters.as_dict(), {}))
+                    except ResolveError as e:
+                        raise ClassNameResolveError(klass, nodename, entity.uri)
             # class not seen or class on a list of global classes (always (re)loaded)
             if klass not in seen or self._gcl_r.match(klass):
                 try:
@@ -125,13 +140,13 @@
                         if self._cnf_r.match(klass):
                             if self._settings.ignore_class_notfound_warning:
                                 # TODO, add logging handler
-                                print >>sys.stderr, "[WARNING] Reclass class not found: '%s'. Skipped!" % klass
+                                print("[WARNING] Reclass class not found: '%s'. Skipped!" % klass, file=sys.stderr)
                             continue
                     e.nodename = nodename
                     e.uri = entity.uri
                     raise
 
-                descent = self._recurse_entity(class_entity, seen=seen,
+                descent = self._recurse_entity(class_entity, context=merge_base, seen=seen,
                                                nodename=nodename, environment=environment)
                 # on every iteration, we merge the result of the recursive
                 # descent into what we have so far…
@@ -146,7 +161,7 @@
 
     def _get_automatic_parameters(self, nodename, environment):
         if self._settings.automatic_parameters:
-            return Parameters({ '_reclass_': { 'name': { 'full': nodename, 'short': str.split(nodename, '.')[0] },
+            return Parameters({ '_reclass_': { 'name': { 'full': nodename, 'short': nodename.split('.')[0] },
                                                'environment': environment } }, self._settings, '__auto__')
         else:
             return Parameters({}, self._settings, '')
@@ -169,6 +184,8 @@
                     node = self._node_entity(nodename)
                 except ClassNotFound as e:
                     raise InvQueryClassNotFound(e)
+                except ClassNameResolveError as e:
+                    raise InvQueryClassNameResolveError(e)
                 if queries is None:
                     try:
                         node.interpolate_exports()
@@ -196,8 +213,8 @@
         seen = {}
         merge_base = self._recurse_entity(base_entity, seen=seen, nodename=nodename,
                                           environment=node_entity.environment)
-        return self._recurse_entity(node_entity, merge_base, seen=seen, nodename=nodename,
-                                    environment=node_entity.environment)
+        return self._recurse_entity(node_entity, merge_base=merge_base, context=merge_base, seen=seen,
+                                    nodename=nodename, environment=node_entity.environment)
 
     def _nodeinfo(self, nodename, inventory):
         try:
diff --git a/reclass/datatypes/__init__.py b/reclass/datatypes/__init__.py
index 48c4a8b..78c110b 100644
--- a/reclass/datatypes/__init__.py
+++ b/reclass/datatypes/__init__.py
@@ -6,6 +6,11 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 from .applications import Applications
 from .classes import Classes
 from .entity import Entity
diff --git a/reclass/datatypes/applications.py b/reclass/datatypes/applications.py
index 3c7afce..8c6ed15 100644
--- a/reclass/datatypes/applications.py
+++ b/reclass/datatypes/applications.py
@@ -6,6 +6,11 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 
 from .classes import Classes
 
@@ -61,4 +66,4 @@
         contents = self._items + \
                 ['%s%s' % (self._negation_prefix, i) for i in self._negations]
         return "%s(%r, %r)" % (self.__class__.__name__, contents,
-                               self._negation_prefix)
+                               str(self._negation_prefix))
diff --git a/reclass/datatypes/classes.py b/reclass/datatypes/classes.py
index 090ed70..33d9b93 100644
--- a/reclass/datatypes/classes.py
+++ b/reclass/datatypes/classes.py
@@ -6,6 +6,15 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
+#try:
+#    from types import StringTypes
+#except ImportError:
+#    StringTypes = (str, )
 
 import six
 import os
@@ -52,6 +61,7 @@
             self.append_if_new(i)
 
     def _assert_is_string(self, item):
+        #if not isinstance(item, StringTypes):
         if not isinstance(item, six.string_types):
             raise TypeError('%s instances can only contain strings, '\
                             'not %s' % (self.__class__.__name__, type(item)))
diff --git a/reclass/datatypes/entity.py b/reclass/datatypes/entity.py
index b43ac72..38360b5 100644
--- a/reclass/datatypes/entity.py
+++ b/reclass/datatypes/entity.py
@@ -6,6 +6,11 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 from .classes import Classes
 from .applications import Applications
 from .exports import Exports
diff --git a/reclass/datatypes/exports.py b/reclass/datatypes/exports.py
index 971befa..7f21295 100644
--- a/reclass/datatypes/exports.py
+++ b/reclass/datatypes/exports.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass (http://github.com/madduck/reclass)
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import copy
 
diff --git a/reclass/datatypes/parameters.py b/reclass/datatypes/parameters.py
index f9f116c..bedad88 100644
--- a/reclass/datatypes/parameters.py
+++ b/reclass/datatypes/parameters.py
@@ -7,6 +7,16 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
+#try:
+#    from types import StringTypes
+#except ImportError:
+#    StringTypes = (str, )
+
 import copy
 import sys
 import types
@@ -44,7 +54,7 @@
     functionality and does not try to be a really mapping object.
     '''
 
-    def __init__(self, mapping, settings, uri, merge_initialise = True):
+    def __init__(self, mapping, settings, uri, parse_strings=True):
         self._settings = settings
         self._base = {}
         self._uri = uri
@@ -54,14 +64,12 @@
         self._resolve_errors = ResolveErrorList()
         self._needs_all_envs = False
         self._keep_overrides = False
+        self._parse_strings = parse_strings
         if mapping is not None:
-            if merge_initialise:
-                # we initialise by merging
-                self._keep_overrides = True
-                self.merge(mapping)
-                self._keep_overrides = False
-            else:
-                self._base = copy.deepcopy(mapping)
+            # we initialise by merging
+            self._keep_overrides = True
+            self.merge(mapping)
+            self._keep_overrides = False
 
     #delimiter = property(lambda self: self._delimiter)
 
@@ -103,7 +111,7 @@
             return value
         else:
             try:
-                return Value(value, self._settings, self._uri)
+                return Value(value, self._settings, self._uri, parse_string=self._parse_strings)
             except InterpolationError as e:
                 e.context = str(path)
                 raise
@@ -132,7 +140,8 @@
         elif isinstance(new, ValueList):
             values.extend(new)
         else:
-            values.append(Value(new, self._settings, self._uri))
+            values.append(Value(new, self._settings, self._uri, parse_string=self._parse_strings))
+            
         return values
 
     def _merge_dict(self, cur, new, path):
@@ -157,6 +166,9 @@
         ret = cur
         for (key, newvalue) in iteritems(new):
             if key.startswith(self._settings.dict_key_override_prefix) and not self._keep_overrides:
+                if not isinstance(newvalue, Value):
+                    newvalue = Value(newvalue, self._settings, self._uri, parse_string=self._parse_strings)
+                newvalue.overwrite = True
                 ret[key.lstrip(self._settings.dict_key_override_prefix)] = newvalue
             else:
                 ret[key] = self._merge_recurse(ret.get(key), newvalue, path.new_subpath(key))
@@ -189,7 +201,7 @@
         else:
             return self._update_value(cur, new)
 
-    def merge(self, other, wrap=True):
+    def merge(self, other):
         """Merge function (public edition).
 
         Call _merge_recurse on self with either another Parameter object or a
@@ -205,15 +217,9 @@
 
         self._unrendered = None
         if isinstance(other, dict):
-            if wrap:
-                wrapped = self._wrap_dict(other, DictPath(self._settings.delimiter))
-            else:
-                wrapped = copy.deepcopy(other)
+            wrapped = self._wrap_dict(other, DictPath(self._settings.delimiter))
         elif isinstance(other, self.__class__):
-            if wrap:
-                wrapped = self._wrap_dict(other._base, DictPath(self._settings.delimiter))
-            else:
-                wrapped = copy.deepcopy(other._base)
+            wrapped = self._wrap_dict(other._base, DictPath(self._settings.delimiter))
         else:
             raise TypeError('Cannot merge %s objects into %s' % (type(other),
                             self.__class__.__name__))
diff --git a/reclass/datatypes/tests/__init__.py b/reclass/datatypes/tests/__init__.py
index e69de29..9aaaf25 100644
--- a/reclass/datatypes/tests/__init__.py
+++ b/reclass/datatypes/tests/__init__.py
@@ -0,0 +1,5 @@
+# -*- coding: utf-8
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
diff --git a/reclass/datatypes/tests/test_applications.py b/reclass/datatypes/tests/test_applications.py
index 6ae07cc..5c896f0 100644
--- a/reclass/datatypes/tests/test_applications.py
+++ b/reclass/datatypes/tests/test_applications.py
@@ -6,8 +6,14 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 from reclass.datatypes import Applications, Classes
 import unittest
+
 try:
     import unittest.mock as mock
 except ImportError:
diff --git a/reclass/datatypes/tests/test_classes.py b/reclass/datatypes/tests/test_classes.py
index 33d179f..8d396e0 100644
--- a/reclass/datatypes/tests/test_classes.py
+++ b/reclass/datatypes/tests/test_classes.py
@@ -6,9 +6,15 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 from reclass.datatypes import Classes
 from reclass.datatypes.classes import INVALID_CHARACTERS_FOR_CLASSNAMES
 import unittest
+
 try:
     import unittest.mock as mock
 except ImportError:
diff --git a/reclass/datatypes/tests/test_entity.py b/reclass/datatypes/tests/test_entity.py
index f398d51..b09e904 100644
--- a/reclass/datatypes/tests/test_entity.py
+++ b/reclass/datatypes/tests/test_entity.py
@@ -6,11 +6,16 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from reclass.settings import Settings
 from reclass.datatypes import Entity, Classes, Parameters, Applications, Exports
 from reclass.errors import ResolveError
 import unittest
+
 try:
     import unittest.mock as mock
 except ImportError:
diff --git a/reclass/datatypes/tests/test_exports.py b/reclass/datatypes/tests/test_exports.py
index 33eccbe..6a6dcde 100644
--- a/reclass/datatypes/tests/test_exports.py
+++ b/reclass/datatypes/tests/test_exports.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass (http://github.com/madduck/reclass)
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from reclass.settings import Settings
 from reclass.datatypes import Exports, Parameters
diff --git a/reclass/datatypes/tests/test_parameters.py b/reclass/datatypes/tests/test_parameters.py
index b5dc243..fb4a11b 100644
--- a/reclass/datatypes/tests/test_parameters.py
+++ b/reclass/datatypes/tests/test_parameters.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import copy
 
@@ -15,6 +19,7 @@
 from reclass.datatypes import Parameters
 from reclass.errors import InfiniteRecursionError, InterpolationError, ResolveError, ResolveErrorList
 import unittest
+
 try:
     import unittest.mock as mock
 except ImportError:
@@ -643,5 +648,38 @@
         p1.interpolate()
         self.assertEqual(p1.as_dict(), r)
 
+    def test_complex_overwrites_1(self):
+        # find a better name for this test
+        p1 = Parameters({ 'test': { 'dict': { 'a': '${values:one}', 'b': '${values:two}' } },
+                          'values': { 'one': 1, 'two': 2, 'three': { 'x': 'X', 'y': 'Y' } } }, SETTINGS, '')
+        p2 = Parameters({ 'test': { 'dict': { 'c': '${values:two}' } } }, SETTINGS, '')
+        p3 = Parameters({ 'test': { 'dict': { '~b': '${values:three}' } } }, SETTINGS, '')
+        r = {'test': {'dict': {'a': 1, 'b': {'x': 'X', 'y': 'Y'}, 'c': 2}}, 'values': {'one': 1, 'three': {'x': 'X', 'y': 'Y'}, 'two': 2} }
+        p2.merge(p3)
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_escaped_string_overwrites(self):
+        p1 = Parameters({ 'test': '\${not_a_ref}' }, SETTINGS, '')
+        p2 = Parameters({ 'test': '\${also_not_a_ref}' }, SETTINGS, '')
+        r = { 'test': '${also_not_a_ref}' }
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_escaped_string_in_ref_dict_overwrite(self):
+        p1 = Parameters({'a': { 'one': '\${not_a_ref}' }, 'b': { 'two': '\${also_not_a_ref}' }}, SETTINGS, '')
+        p2 = Parameters({'c': '${a}'}, SETTINGS, '')
+        p3 = Parameters({'c': '${b}'}, SETTINGS, '')
+        p4 = Parameters({'c': { 'one': '\${again_not_a_ref}' } }, SETTINGS, '')
+        r = {'a': {'one': '${not_a_ref}'}, 'b': {'two': '${also_not_a_ref}'}, 'c': {'one': '${again_not_a_ref}', 'two': '${also_not_a_ref}'}}
+        p1.merge(p2)
+        p1.merge(p3)
+        p1.merge(p4)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/reclass/defaults.py b/reclass/defaults.py
index ccd3db9..19592c6 100644
--- a/reclass/defaults.py
+++ b/reclass/defaults.py
@@ -6,6 +6,11 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 import os, sys
 from .version import RECLASS_NAME
 
diff --git a/reclass/errors.py b/reclass/errors.py
index a96c47b..800a2f8 100644
--- a/reclass/errors.py
+++ b/reclass/errors.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import posix, sys
 import traceback
@@ -39,14 +43,12 @@
     def exit_with_message(self, out=sys.stderr):
         if self._full_traceback:
             t, v, tb = sys.exc_info()
-            print >>out, 'Full Traceback:'
+            print('Full Traceback', file=out)
             for l in traceback.format_tb(tb):
-                print >>out, l,
-            print >>out
+                print(l, file=out)
         if self._traceback:
-            print >>out, self._traceback
-        print >>out, self.message
-        print >>out
+            print(self._traceback, file=out)
+        print(self.message, file=out)
         sys.exit(self.rc)
 
 
@@ -158,6 +160,17 @@
         return msg
 
 
+class ClassNameResolveError(InterpolationError):
+    def __init__(self, classname, nodename, uri):
+        super(ClassNameResolveError, self).__init__(msg=None, uri=uri, nodename=nodename)
+        self.name = classname
+
+    def _get_error_message(self):
+        msg = [ 'In {0}'.format(self.uri),
+                'Class name {0} not resolvable'.format(self.name) ]
+        return msg
+
+
 class InvQueryClassNotFound(InterpolationError):
 
     def __init__(self, classNotFoundError, nodename=''):
@@ -172,6 +185,19 @@
         return msg
 
 
+class InvQueryClassNameResolveError(InterpolationError):
+    def __init__(self, classNameResolveError, nodename=''):
+        super(InvQueryClassNameResolveError, self).__init__(msg=None, nodename=nodename)
+        self.classNameResolveError = classNameResolveError
+        self._traceback = self.classNameResolveError._traceback
+
+    def _get_error_message(self):
+        msg = [ 'Inventory Queries:',
+                '-> {0}'.format(self.classNameResolveError.nodename) ]
+        msg.append(self.classNameResolveError._get_error_message())
+        return msg
+
+
 class ResolveError(InterpolationError):
 
     def __init__(self, reference, uri=None, context=None):
diff --git a/reclass/output/__init__.py b/reclass/output/__init__.py
index 42fdb0b..000952c 100644
--- a/reclass/output/__init__.py
+++ b/reclass/output/__init__.py
@@ -6,7 +6,10 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
-
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 class OutputterBase(object):
 
@@ -14,7 +17,7 @@
         pass
 
     def dump(self, data, pretty_print=False):
-        raise NotImplementedError('dump() method not implemented.')
+        raise NotImplementedError("dump() method not implemented.")
 
 
 class OutputLoader(object):
@@ -24,7 +27,7 @@
         try:
             self._module = __import__(self._name, globals(), locals(), self._name)
         except ImportError:
-            raise NotImplementedError
+            raise NotImplementedError()
 
     def load(self, attr='Outputter'):
         klass = getattr(self._module, attr, None)
diff --git a/reclass/output/json_outputter.py b/reclass/output/json_outputter.py
index 8c79039..5d4cfd4 100644
--- a/reclass/output/json_outputter.py
+++ b/reclass/output/json_outputter.py
@@ -6,9 +6,15 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 from reclass.output import OutputterBase
 import json
 
+
 class Outputter(OutputterBase):
 
     def dump(self, data, pretty_print=False, no_refs=False):
diff --git a/reclass/output/yaml_outputter.py b/reclass/output/yaml_outputter.py
index 9a0d098..05519c6 100644
--- a/reclass/output/yaml_outputter.py
+++ b/reclass/output/yaml_outputter.py
@@ -6,18 +6,27 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 from reclass.output import OutputterBase
 import yaml
 
+_SafeDumper = yaml.CSafeDumper if yaml.__with_libyaml__ else yaml.SafeDumper
+
+
 class Outputter(OutputterBase):
 
     def dump(self, data, pretty_print=False, no_refs=False):
         if (no_refs):
             return yaml.dump(data, default_flow_style=not pretty_print, Dumper=ExplicitDumper)
         else:
-            return yaml.dump(data, default_flow_style=not pretty_print)
+            return yaml.dump(data, default_flow_style=not pretty_print, Dumper=_SafeDumper)
 
-class ExplicitDumper(yaml.SafeDumper):
+
+class ExplicitDumper(_SafeDumper):
     """
     A dumper that will never emit aliases.
     """
diff --git a/reclass/settings.py b/reclass/settings.py
index a33b742..af6c76d 100644
--- a/reclass/settings.py
+++ b/reclass/settings.py
@@ -1,11 +1,15 @@
+# -*- coding: utf-8
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 import copy
 import reclass.values.parser_funcs
 from reclass.defaults import *
 
-try:
-    basestring
-except NameError:
-    basestring = str
+from six import string_types
 
 class Settings(object):
 
@@ -27,7 +31,7 @@
         self.ignore_class_notfound = options.get('ignore_class_notfound', OPT_IGNORE_CLASS_NOTFOUND)
 
         self.ignore_class_notfound_regexp = options.get('ignore_class_notfound_regexp', OPT_IGNORE_CLASS_NOTFOUND_REGEXP)
-        if isinstance(self.ignore_class_notfound_regexp, basestring):
+        if isinstance(self.ignore_class_notfound_regexp, string_types):
             self.ignore_class_notfound_regexp = [ self.ignore_class_notfound_regexp ]
 
         self.ignore_class_notfound_warning = options.get('ignore_class_notfound_warning', OPT_IGNORE_CLASS_NOTFOUND_WARNING)
diff --git a/reclass/storage/__init__.py b/reclass/storage/__init__.py
index f49ac16..3b46a2a 100644
--- a/reclass/storage/__init__.py
+++ b/reclass/storage/__init__.py
@@ -6,6 +6,11 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 
 class NodeStorageBase(object):
 
diff --git a/reclass/storage/common.py b/reclass/storage/common.py
index 6a77fc8..7de71d0 100644
--- a/reclass/storage/common.py
+++ b/reclass/storage/common.py
@@ -1,3 +1,9 @@
+# -*- coding: utf-8
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 import os
 
 class NameMangler:
diff --git a/reclass/storage/loader.py b/reclass/storage/loader.py
index 10ca74c..aab554a 100644
--- a/reclass/storage/loader.py
+++ b/reclass/storage/loader.py
@@ -6,16 +6,20 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
-import importlib
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
+from importlib import import_module
 
 class StorageBackendLoader(object):
 
     def __init__(self, storage_name):
-        self._name = 'reclass.storage.' + storage_name
+        self._name = str('reclass.storage.' + storage_name)
         try:
-            self._module = importlib.import_module(self._name)
-        except ImportError:
+            self._module = import_module(self._name)
+        except ImportError as e:
             raise NotImplementedError
 
     def load(self, klassname='ExternalNodeStorage'):
diff --git a/reclass/storage/memcache_proxy.py b/reclass/storage/memcache_proxy.py
index 8c5e441..cd90fdd 100644
--- a/reclass/storage/memcache_proxy.py
+++ b/reclass/storage/memcache_proxy.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from reclass.storage import NodeStorageBase
 
diff --git a/reclass/storage/mixed/__init__.py b/reclass/storage/mixed/__init__.py
index 990c931..6324c74 100644
--- a/reclass/storage/mixed/__init__.py
+++ b/reclass/storage/mixed/__init__.py
@@ -2,6 +2,10 @@
 # -*- coding: utf-8 -*-
 #
 # This file is part of reclass
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import collections
 import copy
diff --git a/reclass/storage/tests/__init__.py b/reclass/storage/tests/__init__.py
index e69de29..9aaaf25 100644
--- a/reclass/storage/tests/__init__.py
+++ b/reclass/storage/tests/__init__.py
@@ -0,0 +1,5 @@
+# -*- coding: utf-8
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
diff --git a/reclass/storage/tests/test_loader.py b/reclass/storage/tests/test_loader.py
index 6bef87f..12cdec3 100644
--- a/reclass/storage/tests/test_loader.py
+++ b/reclass/storage/tests/test_loader.py
@@ -6,10 +6,16 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 from reclass.storage.loader import StorageBackendLoader
 
 import unittest
 
+
 class TestLoader(unittest.TestCase):
 
     def test_load(self):
diff --git a/reclass/storage/tests/test_memcache_proxy.py b/reclass/storage/tests/test_memcache_proxy.py
index a47c29d..24acf20 100644
--- a/reclass/storage/tests/test_memcache_proxy.py
+++ b/reclass/storage/tests/test_memcache_proxy.py
@@ -6,17 +6,23 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from reclass.settings import Settings
 from reclass.storage.memcache_proxy import MemcacheProxy
 from reclass.storage import NodeStorageBase
 
 import unittest
+
 try:
     import unittest.mock as mock
 except ImportError:
     import mock
 
+
 class TestMemcacheProxy(unittest.TestCase):
 
     def setUp(self):
diff --git a/reclass/storage/tests/test_yamldata.py b/reclass/storage/tests/test_yamldata.py
index d8129ce..5c48db6 100644
--- a/reclass/storage/tests/test_yamldata.py
+++ b/reclass/storage/tests/test_yamldata.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass (http://github.com/madduck/reclass)
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from reclass.storage.yamldata import YamlData
 
diff --git a/reclass/storage/yaml_fs/__init__.py b/reclass/storage/yaml_fs/__init__.py
index 83f3666..a102f31 100644
--- a/reclass/storage/yaml_fs/__init__.py
+++ b/reclass/storage/yaml_fs/__init__.py
@@ -6,6 +6,11 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 import os, sys
 import fnmatch
 import yaml
@@ -21,7 +26,7 @@
 STORAGE_NAME = 'yaml_fs'
 
 def vvv(msg):
-    #print >>sys.stderr, msg
+    #print(msg, file=sys.stderr)
     pass
 
 def path_mangler(inventory_base_uri, nodes_uri, classes_uri):
diff --git a/reclass/storage/yaml_fs/directory.py b/reclass/storage/yaml_fs/directory.py
index 614e1c3..a8916b3 100644
--- a/reclass/storage/yaml_fs/directory.py
+++ b/reclass/storage/yaml_fs/directory.py
@@ -6,6 +6,11 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 import os
 from reclass.errors import NotFoundError
 
@@ -13,7 +18,7 @@
 FILE_EXTENSION = '.yml'
 
 def vvv(msg):
-    #print >>sys.stderr, msg
+    #print(msg, file=sys.stderr)
     pass
 
 
diff --git a/reclass/storage/yaml_git/__init__.py b/reclass/storage/yaml_git/__init__.py
index 86c1247..c26ef77 100644
--- a/reclass/storage/yaml_git/__init__.py
+++ b/reclass/storage/yaml_git/__init__.py
@@ -2,6 +2,10 @@
 # -*- coding: utf-8 -*-
 #
 # This file is part of reclass
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import collections
 import distutils.version
diff --git a/reclass/storage/yamldata.py b/reclass/storage/yamldata.py
index ac3dcb9..a861154 100644
--- a/reclass/storage/yamldata.py
+++ b/reclass/storage/yamldata.py
@@ -6,11 +6,18 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 from reclass import datatypes
 import yaml
 import os
 from reclass.errors import NotFoundError
 
+_SafeLoader = yaml.CSafeLoader if yaml.__with_libyaml__ else yaml.SafeLoader
+
 class YamlData(object):
 
     @classmethod
@@ -23,7 +30,7 @@
             raise NotFoundError('Cannot open: %s' % abs_path)
         y = cls('yaml_fs://{0}'.format(abs_path))
         with open(abs_path) as fp:
-            data = yaml.safe_load(fp)
+            data = yaml.load(fp, Loader=_SafeLoader)
             if data is not None:
                 y._data = data
         return y
@@ -32,7 +39,7 @@
     def from_string(cls, string, uri):
         ''' Initialise yaml data from a string '''
         y = cls(uri)
-        data = yaml.safe_load(string)
+        data = yaml.load(string, Loader=_SafeLoader)
         if data is not None:
             y._data = data
         return y
diff --git a/reclass/tests/__init__.py b/reclass/tests/__init__.py
index e69de29..9aaaf25 100644
--- a/reclass/tests/__init__.py
+++ b/reclass/tests/__init__.py
@@ -0,0 +1,5 @@
+# -*- coding: utf-8
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
diff --git a/reclass/tests/test_core.py b/reclass/tests/test_core.py
index 9225756..679d6ca 100644
--- a/reclass/tests/test_core.py
+++ b/reclass/tests/test_core.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass (http://github.com/madduck/reclass)
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import os
 
diff --git a/reclass/utils/__init__.py b/reclass/utils/__init__.py
index e69de29..9aaaf25 100644
--- a/reclass/utils/__init__.py
+++ b/reclass/utils/__init__.py
@@ -0,0 +1,5 @@
+# -*- coding: utf-8
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
diff --git a/reclass/utils/dictpath.py b/reclass/utils/dictpath.py
index dfb8b32..39b9572 100644
--- a/reclass/utils/dictpath.py
+++ b/reclass/utils/dictpath.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import six
 import re
diff --git a/reclass/utils/tests/__init__.py b/reclass/utils/tests/__init__.py
index e69de29..9aaaf25 100644
--- a/reclass/utils/tests/__init__.py
+++ b/reclass/utils/tests/__init__.py
@@ -0,0 +1,5 @@
+# -*- coding: utf-8
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
diff --git a/reclass/utils/tests/test_dictpath.py b/reclass/utils/tests/test_dictpath.py
index 972dc91..6fbb6b7 100644
--- a/reclass/utils/tests/test_dictpath.py
+++ b/reclass/utils/tests/test_dictpath.py
@@ -6,6 +6,11 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 from reclass.utils.dictpath import DictPath
 import unittest
 
@@ -64,7 +69,7 @@
         delim = '%'
         s = 'a:b\:b:c'
         p = DictPath(delim, s)
-        self.assertEqual('%r' % p, 'DictPath(%r, %r)' % (delim, s))
+        self.assertEqual('%r' % p, "DictPath(%r, %r)" % (delim, str(s)))
 
     def test_str(self):
         s = 'a:b\:b:c'
diff --git a/reclass/values/__init__.py b/reclass/values/__init__.py
index e69de29..9aaaf25 100644
--- a/reclass/values/__init__.py
+++ b/reclass/values/__init__.py
@@ -0,0 +1,5 @@
+# -*- coding: utf-8
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
diff --git a/reclass/values/compitem.py b/reclass/values/compitem.py
index 765b323..7928e6f 100644
--- a/reclass/values/compitem.py
+++ b/reclass/values/compitem.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from reclass.settings import Settings
 from .item import Item
@@ -39,6 +43,21 @@
     def get_references(self):
         return self._refs
 
+    def merge_over(self, item):
+        if item.type == Item.SCALAR or item.type == Item.COMPOSITE:
+            return self
+        elif item.type == Item.LIST:
+            if self._settings.allow_scalar_over_list or (self._settings.allow_none_override and self._value in [None, 'none', 'None']):
+                return self
+            else:
+                raise TypeError('allow scalar over list = False: cannot merge %s over %s' % (repr(self), repr(item)))
+        elif item.type == Item.DICTIONARY:
+            if self._settings.allow_scalar_over_dict or (self._settings.allow_none_override and self._value in [None, 'none', 'None']):
+                return self
+            else:
+                raise TypeError('allow scalar over dict = False: cannot merge %s over %s' % (repr(self), repr(item)))
+        raise TypeError('Cannot merge %s over %s' % (repr(self), repr(item)))
+
     def render(self, context, inventory):
         # Preserve type if only one item
         if len(self._items) == 1:
diff --git a/reclass/values/dictitem.py b/reclass/values/dictitem.py
index 555bd8f..76cefe2 100644
--- a/reclass/values/dictitem.py
+++ b/reclass/values/dictitem.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from reclass.settings import Settings
 from .item import Item
diff --git a/reclass/values/invitem.py b/reclass/values/invitem.py
index 970321b..37a35cf 100644
--- a/reclass/values/invitem.py
+++ b/reclass/values/invitem.py
@@ -3,11 +3,15 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import copy
 import pyparsing as pp
 
-from six import iteritems
+from six import iteritems, string_types
 
 from .item import Item
 from reclass.settings import Settings
@@ -90,7 +94,7 @@
             raise ResolveError(str(path))
 
     def _get_vars(self, var, export, parameter, value):
-        if isinstance(var, str):
+        if isinstance(var, string_types):
             path = DictPath(self._delimiter, var)
             if path.path[0].lower() == 'exports':
                 export = path
diff --git a/reclass/values/item.py b/reclass/values/item.py
index 57fd0e3..bc507f4 100644
--- a/reclass/values/item.py
+++ b/reclass/values/item.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from reclass.utils.dictpath import DictPath
 
diff --git a/reclass/values/listitem.py b/reclass/values/listitem.py
index 1829e32..8f1a21d 100644
--- a/reclass/values/listitem.py
+++ b/reclass/values/listitem.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from .item import Item
 from reclass.settings import Settings
diff --git a/reclass/values/parser.py b/reclass/values/parser.py
index a8adcf0..914e825 100644
--- a/reclass/values/parser.py
+++ b/reclass/values/parser.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import pyparsing as pp
 
diff --git a/reclass/values/parser_funcs.py b/reclass/values/parser_funcs.py
index bd5a1ba..46db7cc 100644
--- a/reclass/values/parser_funcs.py
+++ b/reclass/values/parser_funcs.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import pyparsing as pp
 
diff --git a/reclass/values/refitem.py b/reclass/values/refitem.py
index 3e3341c..d24eeee 100644
--- a/reclass/values/refitem.py
+++ b/reclass/values/refitem.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from .item import Item
 from reclass.defaults import REFERENCE_SENTINELS
diff --git a/reclass/values/scaitem.py b/reclass/values/scaitem.py
index 9de5681..f3057cb 100644
--- a/reclass/values/scaitem.py
+++ b/reclass/values/scaitem.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from reclass.settings import Settings
 from .item import Item
@@ -18,7 +22,7 @@
         return self._value
 
     def merge_over(self, item):
-        if item.type == Item.SCALAR:
+        if item.type == Item.SCALAR or item.type == Item.COMPOSITE:
             return self
         elif item.type == Item.LIST:
             if self._settings.allow_scalar_over_list or (self._settings.allow_none_override and self._value is None):
diff --git a/reclass/values/tests/__init__.py b/reclass/values/tests/__init__.py
index e69de29..16d1248 100644
--- a/reclass/values/tests/__init__.py
+++ b/reclass/values/tests/__init__.py
@@ -0,0 +1,7 @@
+#
+# -*- coding: utf-8
+#
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
diff --git a/reclass/values/tests/test_value.py b/reclass/values/tests/test_value.py
index 84403d3..4853340 100644
--- a/reclass/values/tests/test_value.py
+++ b/reclass/values/tests/test_value.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import pyparsing as pp
 
diff --git a/reclass/values/value.py b/reclass/values/value.py
index 74ef272..f87a9b4 100644
--- a/reclass/values/value.py
+++ b/reclass/values/value.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from .parser import Parser
 from .dictitem import DictItem
@@ -10,19 +14,25 @@
 from .scaitem import ScaItem
 from reclass.errors import InterpolationError
 
+from six import string_types
+
 class Value(object):
 
     _parser = Parser()
 
-    def __init__(self, value, settings, uri):
+    def __init__(self, value, settings, uri, parse_string=True):
         self._settings = settings
         self._uri = uri
-        if isinstance(value, str):
-            try:
-                self._item = self._parser.parse(value, self._settings)
-            except InterpolationError as e:
-                e.uri = self._uri
-                raise
+        self._overwrite = False
+        if isinstance(value, string_types):
+            if parse_string:
+                try:
+                    self._item = self._parser.parse(value, self._settings)
+                except InterpolationError as e:
+                    e.uri = self._uri
+                    raise
+            else:
+                self._item = ScaItem(value, self._settings)
         elif isinstance(value, list):
             self._item = ListItem(value, self._settings)
         elif isinstance(value, dict):
@@ -30,6 +40,14 @@
         else:
             self._item = ScaItem(value, self._settings)
 
+    @property
+    def overwrite(self):
+        return self._overwrite
+
+    @overwrite.setter
+    def overwrite(self, overwrite):
+        self._overwrite = overwrite
+
     def uri(self):
         return self._uri
 
diff --git a/reclass/values/valuelist.py b/reclass/values/valuelist.py
index fc0eaad..8b8dd51 100644
--- a/reclass/values/valuelist.py
+++ b/reclass/values/valuelist.py
@@ -3,6 +3,10 @@
 #
 # This file is part of reclass
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from __future__ import print_function
 
@@ -35,6 +39,9 @@
         self.assembleRefs()
         self._check_for_inv_query()
 
+    def uri(self):
+        return '; '.join([ x.uri() for x in self._values ])
+
     def has_references(self):
         return len(self._refs) > 0
 
@@ -104,14 +111,14 @@
                 else:
                     raise e
 
-            if output is None:
+            if output is None or value.overwrite:
                 output = new
                 deepCopied = False
             else:
                 if isinstance(output, dict) and isinstance(new, dict):
-                    p1 = Parameters(output, self._settings, None, merge_initialise = False)
-                    p2 = Parameters(new, self._settings, None, merge_initialise = False)
-                    p1.merge(p2, wrap=False)
+                    p1 = Parameters(output, self._settings, None, parse_strings=False)
+                    p2 = Parameters(new, self._settings, None, parse_strings=False)
+                    p1.merge(p2)
                     output = p1.as_dict()
                     continue
                 elif isinstance(output, list) and isinstance(new, list):
@@ -124,6 +131,7 @@
                     raise TypeError('Cannot merge %s over %s' % (repr(self._values[n]), repr(self._values[n-1])))
                 else:
                     output = new
+                    deepCopied = False
 
         if isinstance(output, (dict, list)) and last_error is not None:
             raise last_error
diff --git a/reclass/version.py b/reclass/version.py
index 90c2cb7..ccf6e96 100644
--- a/reclass/version.py
+++ b/reclass/version.py
@@ -6,9 +6,14 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 RECLASS_NAME = 'reclass'
 DESCRIPTION = 'merge data by recursive descent down an ancestry hierarchy (forked extended version)'
-VERSION = '1.5.2'
+VERSION = '1.5.4'
 AUTHOR = 'martin f. krafft / Andrew Pickford / salt-formulas community'
 AUTHOR_EMAIL = 'salt-formulas@freelists.org'
 MAINTAINER = 'salt-formulas community'
diff --git a/run_tests.py b/run_tests.py
index 1506945..aeccb57 100755
--- a/run_tests.py
+++ b/run_tests.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–13 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import unittest
 tests = unittest.TestLoader().discover('reclass')
diff --git a/setup.py b/setup.py
index 5b4b8b6..789b0fd 100644
--- a/setup.py
+++ b/setup.py
@@ -6,6 +6,10 @@
 # Copyright © 2007–13 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 from reclass.version import *
 from setuptools import setup, find_packages
diff --git a/test/model/default/classes/first.yml b/test/model/default/classes/first.yml
new file mode 100644
index 0000000..9b72a26
--- /dev/null
+++ b/test/model/default/classes/first.yml
@@ -0,0 +1,32 @@
+parameters:
+  _param:
+    some: param
+    colour: red
+  lab:
+    name: test
+    label: first
+  colour:
+    escaped: \${_param:colour}
+    doubleescaped: \\${_param:colour}
+    unescaped: ${_param:colour}
+  colours:
+    red:
+      name: red
+    blue:
+      name: blue
+  one:
+    a: 1
+    b: 2
+  two:
+    c: 3
+    d: 4
+  three:
+    e: 5
+  list_to_override:
+  - one
+  - two
+  dict_to_override:
+   one: 1
+   two: 2
+
+
diff --git a/test/model/default/classes/lab/env/dev.yml b/test/model/default/classes/lab/env/dev.yml
new file mode 100644
index 0000000..0cce363
--- /dev/null
+++ b/test/model/default/classes/lab/env/dev.yml
@@ -0,0 +1,4 @@
+
+parameters:
+  lab:
+    name: dev
diff --git a/test/model/default/classes/second.yml b/test/model/default/classes/second.yml
new file mode 100644
index 0000000..dab50c7
--- /dev/null
+++ b/test/model/default/classes/second.yml
@@ -0,0 +1,9 @@
+classes:
+- first
+
+parameters:
+  will:
+    warn:
+      at:
+        second: ${_param:notfound}
+  three: ${one}
diff --git a/test/model/default/classes/third.yml b/test/model/default/classes/third.yml
new file mode 100644
index 0000000..135acd4
--- /dev/null
+++ b/test/model/default/classes/third.yml
@@ -0,0 +1,18 @@
+classes:
+- second
+
+parameters:
+  _param:
+    notfound: exist
+  myparam: ${_param:some}
+  will:
+    not:
+      fail:
+        at:
+          tree: ${_param:notfound}
+  three: ${two}
+  empty:
+    list: []
+    dict: {}
+  ~list_to_override: ${empty:list}
+  ~dict_to_override: ${empty:dict}
diff --git a/test/model/default/nodes/reclass.yml b/test/model/default/nodes/reclass.yml
new file mode 100644
index 0000000..94b7519
--- /dev/null
+++ b/test/model/default/nodes/reclass.yml
@@ -0,0 +1,3 @@
+
+classes:
+- third
diff --git a/test/model/default/reclass-config.yml b/test/model/default/reclass-config.yml
new file mode 100644
index 0000000..9d8f30f
--- /dev/null
+++ b/test/model/default/reclass-config.yml
@@ -0,0 +1 @@
+storage_type: yaml_fs
diff --git a/test/model/extensions/classes/first.yml b/test/model/extensions/classes/first.yml
new file mode 100644
index 0000000..96ece27
--- /dev/null
+++ b/test/model/extensions/classes/first.yml
@@ -0,0 +1,6 @@
+parameters:
+  _param:
+    some: param
+  lab:
+    name: test
+    label: first
diff --git a/test/model/extensions/classes/lab/env/dev.yml b/test/model/extensions/classes/lab/env/dev.yml
new file mode 100644
index 0000000..0cce363
--- /dev/null
+++ b/test/model/extensions/classes/lab/env/dev.yml
@@ -0,0 +1,4 @@
+
+parameters:
+  lab:
+    name: dev
diff --git a/test/model/extensions/classes/second.yml b/test/model/extensions/classes/second.yml
new file mode 100644
index 0000000..a9babd3
--- /dev/null
+++ b/test/model/extensions/classes/second.yml
@@ -0,0 +1,8 @@
+classes:
+- first
+
+parameters:
+  will:
+    warn:
+      at:
+        second: ${_param:notfound}
diff --git a/test/model/extensions/classes/third.yml b/test/model/extensions/classes/third.yml
new file mode 100644
index 0000000..20a937c
--- /dev/null
+++ b/test/model/extensions/classes/third.yml
@@ -0,0 +1,13 @@
+classes:
+- missing.class
+- second
+
+parameters:
+  _param:
+    notfound: exist
+  myparam: ${_param:some}
+  will:
+    not:
+      fail:
+        at:
+          tree: ${_param:notfound}
diff --git a/test/model/extensions/nodes/reclass.yml b/test/model/extensions/nodes/reclass.yml
new file mode 100644
index 0000000..94b7519
--- /dev/null
+++ b/test/model/extensions/nodes/reclass.yml
@@ -0,0 +1,3 @@
+
+classes:
+- third
diff --git a/test/model/extensions/reclass-config.yml b/test/model/extensions/reclass-config.yml
new file mode 100644
index 0000000..6e2f101
--- /dev/null
+++ b/test/model/extensions/reclass-config.yml
@@ -0,0 +1,3 @@
+storage_type: yaml_fs
+ignore_class_notfound: True
+ignore_class_regexp: ['.*']