diff --git a/src/__init__.py b/src/__init__.py
new file mode 100644
index 0000000..19d1424
--- /dev/null
+++ b/src/__init__.py
@@ -0,0 +1,13 @@
+# Copyright 2019-present Open Networking Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
diff --git a/src/grpc_client/KEYS.reference.py b/src/grpc_client/KEYS.reference.py
index fd8c776..6453117 100644
--- a/src/grpc_client/KEYS.reference.py
+++ b/src/grpc_client/KEYS.reference.py
@@ -19,57 +19,57 @@
 #########################################################################
 
 TOSCA_KEYS = {
-    'XOSBase': [],
-    'User': ['email'],
-    'Privilege': [],
-    'AddressPool': ['name'],
-    'Controller': ['name'],
-    'ControllerImages': [],
-    'ControllerNetwork': [],
-    'ControllerRole': [],
-    'ControllerSite': [],
-    'ControllerPrivilege': [],
-    'ControllerSitePrivilege': [],
-    'ControllerSlice': [],
-    'ControllerSlicePrivilege': [],
-    'ControllerUser': [],
-    'Deployment': ['name'],
-    'DeploymentPrivilege': [],
-    'DeploymentRole': [],
-    'Diag': ['name'],
-    'Flavor': ['name'],
-    'Image': ['name'],
-    'ImageDeployments': [],
-    'Instance': ['name'],
-    'Network': ['name'],
-    'NetworkParameter': [],
-    'NetworkParameterType': ['name'],
-    'NetworkSlice': ['network', 'slice'],
-    'NetworkTemplate': ['name'],
-    'Node': ['name'],
-    'NodeLabel': ['name'],
-    'Port': [],
-    'Role': [],
-    'Service': ['name'],
-    'ServiceAttribute': ['name'],
-    'ServiceDependency': ['provider_service'],
-    'ServiceMonitoringAgentInfo': ['name'],
-    'ServicePrivilege': [],
-    'ServiceRole': [],
-    'Site': ['name'],
-    'SiteDeployment': ['site', 'deployment'],
-    'SitePrivilege': ['site', 'role'],
-    'SiteRole': [],
-    'Slice': ['name'],
-    'SlicePrivilege': [],
-    'SliceRole': [],
-    'Tag': ['name'],
-    'InterfaceType': ['name'],
-    'ServiceInterface': ['service', 'interface_type'],
-    'ServiceInstance': ['name'],
-    'ServiceInstanceLink': ['provider_service_instance'],
-    'ServiceInstanceAttribute': ['name'],
-    'TenantWithContainer': ['name'],
-    'XOS': ['name'],
-    'XOSGuiExtension': ['name'],
-}
\ No newline at end of file
+    "XOSBase": [],
+    "User": ["email"],
+    "Privilege": [],
+    "AddressPool": ["name"],
+    "Controller": ["name"],
+    "ControllerImages": [],
+    "ControllerNetwork": [],
+    "ControllerRole": [],
+    "ControllerSite": [],
+    "ControllerPrivilege": [],
+    "ControllerSitePrivilege": [],
+    "ControllerSlice": [],
+    "ControllerSlicePrivilege": [],
+    "ControllerUser": [],
+    "Deployment": ["name"],
+    "DeploymentPrivilege": [],
+    "DeploymentRole": [],
+    "Diag": ["name"],
+    "Flavor": ["name"],
+    "Image": ["name"],
+    "ImageDeployments": [],
+    "Instance": ["name"],
+    "Network": ["name"],
+    "NetworkParameter": [],
+    "NetworkParameterType": ["name"],
+    "NetworkSlice": ["network", "slice"],
+    "NetworkTemplate": ["name"],
+    "Node": ["name"],
+    "NodeLabel": ["name"],
+    "Port": [],
+    "Role": [],
+    "Service": ["name"],
+    "ServiceAttribute": ["name"],
+    "ServiceDependency": ["provider_service"],
+    "ServiceMonitoringAgentInfo": ["name"],
+    "ServicePrivilege": [],
+    "ServiceRole": [],
+    "Site": ["name"],
+    "SiteDeployment": ["site", "deployment"],
+    "SitePrivilege": ["site", "role"],
+    "SiteRole": [],
+    "Slice": ["name"],
+    "SlicePrivilege": [],
+    "SliceRole": [],
+    "Tag": ["name"],
+    "InterfaceType": ["name"],
+    "ServiceInterface": ["service", "interface_type"],
+    "ServiceInstance": ["name"],
+    "ServiceInstanceLink": ["provider_service_instance"],
+    "ServiceInstanceAttribute": ["name"],
+    "TenantWithContainer": ["name"],
+    "XOS": ["name"],
+    "XOSGuiExtension": ["name"],
+}
diff --git a/src/grpc_client/__init__.py b/src/grpc_client/__init__.py
index d4e8062..c7879fb 100644
--- a/src/grpc_client/__init__.py
+++ b/src/grpc_client/__init__.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,4 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import absolute_import
 
+from .main import GRPC_Client
+
+__all__ = [
+    'GRPC_Client',
+]
diff --git a/src/grpc_client/main.py b/src/grpc_client/main.py
index 619b43b..314081f 100644
--- a/src/grpc_client/main.py
+++ b/src/grpc_client/main.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,23 +13,27 @@
 # limitations under the License.
 
 
-import functools
-from xosapi.xos_grpc_client import SecureClient, InsecureClient
-from twisted.internet import defer
-from resources import RESOURCES
-from xosconfig import Config
-from twisted.internet import reactor
+from __future__ import absolute_import
 
-from xosconfig import Config
+import functools
+
+from xosapi.xos_grpc_client import InsecureClient, SecureClient
+
 from multistructlog import create_logger
-log = create_logger(Config().get('logging'))
+from twisted.internet import defer, reactor
+from xosconfig import Config
+
+from .resources import RESOURCES
+
+log = create_logger(Config().get("logging"))
+
 
 class GRPC_Client:
     def __init__(self):
         self.client = None
 
-        insecure = Config.get('gprc_endpoint')
-        secure = Config.get('gprc_endpoint')
+        insecure = Config.get("gprc_endpoint")
+        secure = Config.get("gprc_endpoint")
 
         self.grpc_secure_endpoint = secure + ":50051"
         self.grpc_insecure_endpoint = insecure + ":50055"
@@ -55,26 +58,36 @@
         self.client = InsecureClient(endpoint=self.grpc_insecure_endpoint)
         self.client.restart_on_disconnect = True
 
-        self.client.set_reconnect_callback(functools.partial(deferred.callback, self.client))
+        self.client.set_reconnect_callback(
+            functools.partial(deferred.callback, self.client)
+        )
         self.client.start()
 
         return deferred
 
     def create_secure_client(self, username, password, arg):
         """
-        This method will check if this combination of username/password already has stored orm classes in RESOURCES, otherwise create them
+        This method will check if this combination of username/password already
+        has stored orm classes in RESOURCES, otherwise create them
         """
         deferred = defer.Deferred()
         key = "%s~%s" % (username, password)
         if key in RESOURCES:
             reactor.callLater(0, deferred.callback, arg)
         else:
-            local_cert = Config.get('local_cert')
-            client = SecureClient(endpoint=self.grpc_secure_endpoint, username=username, password=password, cacert=local_cert)
+            local_cert = Config.get("local_cert")
+            client = SecureClient(
+                endpoint=self.grpc_secure_endpoint,
+                username=username,
+                password=password,
+                cacert=local_cert,
+            )
             client.restart_on_disconnect = True
             # SecureClient is preceeded by an insecure client, so treat all secure clients as previously connected
             # See CORD-3152
             client.was_connected = True
-            client.set_reconnect_callback(functools.partial(self.setup_resources, client, key, deferred, arg))
+            client.set_reconnect_callback(
+                functools.partial(self.setup_resources, client, key, deferred, arg)
+            )
             client.start()
         return deferred
diff --git a/src/grpc_client/models_accessor.py b/src/grpc_client/models_accessor.py
index 2c96c48..445918a 100644
--- a/src/grpc_client/models_accessor.py
+++ b/src/grpc_client/models_accessor.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,11 +12,22 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from xosconfig import Config
-from multistructlog import create_logger
-log = create_logger(Config().get('logging'))
+from __future__ import absolute_import
 
-from resources import RESOURCES
+from multistructlog import create_logger
+from xosconfig import Config
+
+from .resources import RESOURCES
+
+log = create_logger(Config().get("logging"))
+
+
+class GRPCModelsException(Exception):
+    """
+    Differentiates between exceptions created by GRPCModelsAccessor and other exceptions
+    """
+    pass
+
 
 class GRPCModelsAccessor:
     """
@@ -31,24 +41,31 @@
         """
 
         # NOTE: we need to import this later as it's generated by main.py
-        from KEYS import TOSCA_KEYS
+        from .KEYS import TOSCA_KEYS
 
         # get the key for this model
         try:
             filter_keys = TOSCA_KEYS[class_name]
-        except KeyError, e:
-            raise Exception("[XOS-TOSCA] Model %s doesn't have a tosca_key specified" % (class_name))
+        except KeyError:
+            raise GRPCModelsException(
+                "[XOS-TOSCA] Model %s doesn't have a tosca_key specified" % (class_name)
+            )
 
         if len(filter_keys) == 0:
-            raise Exception("[XOS-TOSCA] Model %s doesn't have a tosca_key specified" % (class_name))
+            raise GRPCModelsException(
+                "[XOS-TOSCA] Model %s doesn't have a tosca_key specified" % (class_name)
+            )
 
         filter = {}
         for k in filter_keys:
             if isinstance(k, str):
                 try:
                     filter[k] = data[k]
-                except KeyError, e:
-                    raise Exception("[XOS-TOSCA] Model %s doesn't have a property for the specified tosca_key (%s)" % (class_name, e))
+                except KeyError as e:
+                    raise GRPCModelsException(
+                        "[XOS-TOSCA] Model %s doesn't have a property for the specified tosca_key (%s)"
+                        % (class_name, e)
+                    )
             elif isinstance(k, list):
                 # one of they keys in this list has to be set
                 one_of_key = None
@@ -57,15 +74,23 @@
                         one_of_key = i
                         one_of_key_val = data[i]
                 if not one_of_key:
-                    raise Exception("[XOS-TOSCA] Model %s doesn't have a property for the specified tosca_key_one_of (%s)" % (class_name, k))
+                    raise GRPCModelsException(
+                        "[XOS-TOSCA] Model %s doesn't have a property for the specified tosca_key_one_of (%s)"
+                        % (class_name, k)
+                    )
                 else:
                     filter[one_of_key] = one_of_key_val
 
         key = "%s~%s" % (username, password)
-        if not key in RESOURCES:
-            raise Exception("[XOS-TOSCA] User '%s' does not have ready resources" % username)
+        if key not in RESOURCES:
+            raise GRPCModelsException(
+                "[XOS-TOSCA] User '%s' does not have ready resources" % username
+            )
         if class_name not in RESOURCES[key]:
-            raise Exception('[XOS-TOSCA] The model you are trying to create (class: %s, properties, %s) is not know by xos-core' % (class_name, str(filter)))
+            raise GRPCModelsException(
+                "[XOS-TOSCA] The model you are trying to create (class: %s, properties, %s) is not know by xos-core"
+                % (class_name, str(filter))
+            )
 
         cls = RESOURCES[key][class_name]
 
@@ -73,15 +98,27 @@
 
         if len(models) == 1:
             model = models[0]
-            log.info("[XOS-Tosca] Model of class %s and properties %s already exist, retrieving instance..." % (class_name, str(filter)), model=model)
+            log.info(
+                "[XOS-TOSCA] Model of class %s and properties %s already exist, retrieving instance..."
+                % (class_name, str(filter)),
+                model=model,
+            )
         elif len(models) == 0:
 
-            if 'must-exist' in data and data['must-exist']:
-                raise Exception("[XOS-TOSCA] Model of class %s and properties %s has property 'must-exist' but cannot be found" % (class_name, str(filter)))
+            if "must-exist" in data and data["must-exist"]:
+                raise GRPCModelsException(
+                    "[XOS-TOSCA] Model of class %s and properties %s has property 'must-exist' but cannot be found"
+                    % (class_name, str(filter))
+                )
 
             model = cls.objects.new()
-            log.info("[XOS-Tosca] Model (%s) is new, creating new instance..." % str(filter))
+            log.info(
+                "[XOS-TOSCA] Model (%s) is new, creating new instance..." % str(filter)
+            )
         else:
-            raise Exception("[XOS-Tosca] Model of class %s and properties %s has multiple instances, I can't handle it" % (class_name, str(filter)))
+            raise GRPCModelsException(
+                "[XOS-TOSCA] Model of class %s and properties %s has multiple instances, I can't handle it"
+                % (class_name, str(filter))
+            )
 
-        return model
\ No newline at end of file
+        return model
diff --git a/src/grpc_client/resources.py b/src/grpc_client/resources.py
index cfe3e2e..88ce137 100644
--- a/src/grpc_client/resources.py
+++ b/src/grpc_client/resources.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -15,4 +14,4 @@
 
 
 # NOTE will add all the resources in this dictionary
-RESOURCES = {}
\ No newline at end of file
+RESOURCES = {}
diff --git a/src/main.py b/src/main.py
index 6b0359d..94955b0 100644
--- a/src/main.py
+++ b/src/main.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,26 +12,28 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import absolute_import
 
 import os
+
+from twisted.internet import defer
 from xosconfig import Config
 from multistructlog import create_logger
 
 current_dir = os.path.dirname(os.path.realpath(__file__))
-config_file = os.path.join(current_dir, 'xos-tosca.config.yaml')
-config_schema = os.path.join(current_dir, 'xos-tosca-config-schema.yaml')
+config_file = os.path.join(current_dir, "xos-tosca.config.yaml")
+config_schema = os.path.join(current_dir, "xos-tosca-config-schema.yaml")
 
 Config.init(config_file, config_schema)
-log = create_logger(Config().get('logging'))
+log = create_logger(Config().get("logging"))
 
-from grpc_client.main import GRPC_Client
-from tosca.generator import TOSCA_Generator
-from web_server.main import TOSCA_WebServer
-from twisted.internet import defer
+# config needs to be init before these imports, thus E402
+from grpc_client import GRPC_Client  # noqa: E402
+from tosca import TOSCA_Generator  # noqa: E402
+from web_server import TOSCA_WebServer  # noqa: E402
 
 
 class Main:
-
     def __init__(self):
         self.grpc_client = None
 
@@ -47,9 +48,11 @@
     def start(self):
         log.info("[XOS-TOSCA] Starting")
 
-        # Remove generated TOSCA and KEYS that may have been downloaded by a previous session. This is done here, rather
-        # than in the generator, to cover the case where the TOSCA engine is restarted and a web request is received
-        # and processed before generate_tosca() has completed. 
+        # Remove generated TOSCA and KEYS that may have been downloaded by a
+        # previous session. This is done here, rather than in the generator, to
+        # cover the case where the TOSCA engine is restarted and a web request
+        # is received and processed before generate_tosca() has completed.
+
         TOSCA_Generator().clean()
         TOSCA_Generator().clean_keys()
 
@@ -60,5 +63,5 @@
         TOSCA_WebServer()
 
 
-if __name__ == '__main__':
-    Main().start()
\ No newline at end of file
+if __name__ == "__main__":
+    Main().start()
diff --git a/src/tosca/__init__.py b/src/tosca/__init__.py
index d4e8062..cbdb48b 100644
--- a/src/tosca/__init__.py
+++ b/src/tosca/__init__.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,4 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import absolute_import
 
+from .generator import TOSCA_Generator
+
+__all__ = [
+    'TOSCA_Generator',
+]
diff --git a/src/tosca/default.py b/src/tosca/default.py
index 4de0975..02d7de4 100644
--- a/src/tosca/default.py
+++ b/src/tosca/default.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,8 +13,12 @@
 # limitations under the License.
 
 
+from __future__ import absolute_import
+
 import os
 
 TOSCA_DEFS_DIR = os.path.dirname(os.path.realpath(__file__)) + "/custom_types"
 TOSCA_RECIPES_DIR = os.path.dirname(os.path.realpath(__file__)) + "/"
-TOSCA_KEYS_DIR = os.path.abspath(os.path.dirname(os.path.realpath(__file__)) + "/../grpc_client")
\ No newline at end of file
+TOSCA_KEYS_DIR = os.path.abspath(
+    os.path.dirname(os.path.realpath(__file__)) + "/../grpc_client"
+)
diff --git a/src/tosca/generator.py b/src/tosca/generator.py
index 1c2dccb..fbaf4e5 100644
--- a/src/tosca/generator.py
+++ b/src/tosca/generator.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,24 +12,30 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from xosconfig import Config
-from multistructlog import create_logger
-log = create_logger(Config().get('logging'))
+from __future__ import absolute_import
 
 import os
-from default import TOSCA_DEFS_DIR, TOSCA_KEYS_DIR
-from xosgenx.generator import XOSProcessor, XOSProcessorArgs
+
 from xosapi.xos_grpc_client import Empty
+from xosgenx.generator import XOSProcessor, XOSProcessorArgs
+
+from multistructlog import create_logger
+from xosconfig import Config
+
+from .default import TOSCA_DEFS_DIR, TOSCA_KEYS_DIR
+
+log = create_logger(Config().get("logging"))
+
 
 current_dir = os.path.dirname(os.path.realpath(__file__))
 
-class TOSCA_Generator:
 
+class TOSCA_Generator:
     def clean(self, dir=TOSCA_DEFS_DIR):
         filesToRemove = [f for f in os.listdir(dir)]
         for f in filesToRemove:
-            if not f.startswith('.'):
-                os.remove(dir + '/' + f)
+            if not f.startswith("."):
+                os.remove(dir + "/" + f)
 
     def clean_keys(self, dir=TOSCA_KEYS_DIR):
         keys_fn = os.path.join(dir, "KEYS.py")
@@ -42,23 +47,27 @@
 
         try:
             xproto = client.utility.GetXproto(Empty())
-            args = XOSProcessorArgs(output = TOSCA_DEFS_DIR,
-                                    inputs = str(xproto.xproto),
-                                    target = os.path.join(current_dir, 'xtarget/tosca.xtarget'),
-                                    write_to_file = 'target')
+            args = XOSProcessorArgs(
+                output=TOSCA_DEFS_DIR,
+                inputs=str(xproto.xproto),
+                target=os.path.join(current_dir, "xtarget/tosca.xtarget"),
+                write_to_file="target",
+            )
             XOSProcessor.process(args)
             log.info("[XOS-TOSCA] Recipes generated in %s" % args.output)
-        except Exception as e:
+        except Exception:
             log.exception("[XOS-TOSCA] Failed to generate TOSCA")
 
         try:
             xproto = client.utility.GetXproto(Empty())
-            args = XOSProcessorArgs(output = TOSCA_KEYS_DIR,
-                                    inputs = str(xproto.xproto),
-                                    target = os.path.join(current_dir, 'xtarget/tosca_keys.xtarget'),
-                                    write_to_file = 'single',
-                                    dest_file = 'KEYS.py')
+            args = XOSProcessorArgs(
+                output=TOSCA_KEYS_DIR,
+                inputs=str(xproto.xproto),
+                target=os.path.join(current_dir, "xtarget/tosca_keys.xtarget"),
+                write_to_file="single",
+                dest_file="KEYS.py",
+            )
             XOSProcessor.process(args)
             log.info("[XOS-TOSCA] TOSCA Keys generated in %s" % args.output)
-        except Exception as e:
+        except Exception:
             log.exception("[XOS-TOSCA] Failed to generate TOSCA Keys")
diff --git a/src/tosca/parser.py b/src/tosca/parser.py
index 3f44c50..6643ac8 100644
--- a/src/tosca/parser.py
+++ b/src/tosca/parser.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,23 +12,24 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import absolute_import
 
+import json
 import os
 from tempfile import NamedTemporaryFile
-from xosconfig import Config
-from multistructlog import create_logger
-log = create_logger(Config().get('logging'))
 
-from toscaparser.tosca_template import ToscaTemplate, ValidationError
-from default import TOSCA_RECIPES_DIR
-from grpc_client.resources import RESOURCES
-from grpc_client.models_accessor import GRPCModelsAccessor
 from grpc._channel import _Rendezvous
-import json
-import traceback
+from grpc_client.models_accessor import GRPCModelsAccessor, GRPCModelsException
+from multistructlog import create_logger
+from toscaparser.tosca_template import ToscaTemplate, ValidationError
+from xosconfig import Config
+
+from .default import TOSCA_RECIPES_DIR
+
+log = create_logger(Config().get("logging"))
+
 
 class TOSCA_Parser:
-
     def compute_dependencies(self, template, models_by_name):
         """
         NOTE this method is augmenting self.template, isn't there a more explicit way to achieve it?
@@ -38,18 +38,18 @@
             nodetemplate.dependencies = []
             nodetemplate.dependencies_names = []
             for reqs in nodetemplate.requirements:
-                for (k,v) in reqs.items():
+                for (k, v) in reqs.items():
                     name = v["node"]
-                    if (name in models_by_name):
+                    if name in models_by_name:
                         nodetemplate.dependencies.append(models_by_name[name])
                         nodetemplate.dependencies_names.append(name)
 
                     # go another level deep, as our requirements can have requirements...
                     # NOTE do we still need to go deep?
-                    for sd_req in v.get("requirements",[]):
+                    for sd_req in v.get("requirements", []):
                         for (sd_req_k, sd_req_v) in sd_req.items():
                             name = sd_req_v["node"]
-                            if (name in models_by_name):
+                            if name in models_by_name:
                                 nodetemplate.dependencies.append(models_by_name[name])
                                 nodetemplate.dependencies_names.append(name)
 
@@ -63,8 +63,8 @@
             values = values | set(v.dependencies_names)
 
         all_nodes = list(keys | values)
-        steps = all_nodes
 
+        steps = all_nodes
 
         # Final order
         order = []
@@ -72,26 +72,26 @@
         # DFS stack, not using recursion
         stack = []
 
-        # Unmarked set
-        unmarked = all_nodes
+        # Unmarked set, alpha sorted to provide determinism not present in dicts
+        unmarked = sorted(all_nodes)
 
         # visiting = [] - skip, don't expect 1000s of nodes, |E|/|V| is small
 
         while unmarked:
             stack.insert(0, unmarked[0])  # push first unmarked
 
-            while (stack):
+            while stack:
                 n = stack[0]
                 add = True
                 try:
                     for m in g[n].dependencies_names:
-                        if (m in unmarked):
+                        if m in unmarked:
                             add = False
                             stack.insert(0, m)
                 except KeyError:
                     pass
-                if (add):
-                    if (n in steps and n not in order):
+                if add:
+                    if n in steps and n not in order:
                         order.append(n)
                     item = stack.pop(0)
                     try:
@@ -99,33 +99,39 @@
                     except ValueError:
                         pass
 
-        noorder = list(set(steps) - set(order))
+        # remove ordred items from steps, then alpha sort unordered items (determinism)
+        noorder = sorted(list(set(steps) - set(order)))
         return order + noorder
 
     @staticmethod
     def populate_model(model, data):
-        for k,v in data.iteritems():
+        for key in sorted(data):
             # NOTE must-exists is a TOSCA implementation choice, remove it before saving the model
-            if k != "must-exist":
+            if key != "must-exist":
                 try:
-                    setattr(model, k, v)
-                except TypeError, e:
-                    raise Exception('Failed to set %s on field %s for class %s, Exception was: "%s"' % (v, k, model.model_name, e))
+                    setattr(model, key, data[key])
+                except TypeError as e:
+                    raise Exception(
+                        'Failed to set %s on field %s for class %s, Exception was: "%s"'
+                        % (data[key], key, model.model_name, e)
+                    )
         return model
 
     @staticmethod
     def _translate_exception(msg):
         readable = []
         for line in msg.splitlines():
-            if line.strip().startswith('MissingRequiredFieldError') or \
-                    line.strip().startswith('UnknownFieldError') or \
-                    line.strip().startswith('ImportError') or \
-                    line.strip().startswith('InvalidTypeError') or \
-                    line.strip().startswith('TypeMismatchError'):
+            if (
+                line.strip().startswith("MissingRequiredFieldError")
+                or line.strip().startswith("UnknownFieldError")
+                or line.strip().startswith("ImportError")
+                or line.strip().startswith("InvalidTypeError")
+                or line.strip().startswith("TypeMismatchError")
+            ):
                 readable.append(line)
 
         if len(readable) > 0:
-            return '\n'.join(readable) + '\n'
+            return "\n".join(readable) + "\n"
         else:
             return msg
 
@@ -147,24 +153,24 @@
     @staticmethod
     def populate_dependencies(model, requirements, saved_models):
         for dep in requirements:
-            class_name = dep.keys()[0]
-            related_model = saved_models[dep[class_name]['node']]
+            class_name = list(dep.keys())[0]
+            related_model = saved_models[dep[class_name]["node"]]
             setattr(model, "%s_id" % class_name, related_model.id)
         return model
 
     @staticmethod
     def add_dependencies(data, requirements, saved_models):
         for dep in requirements:
-            class_name = dep.keys()[0]
-            related_model = saved_models[dep[class_name]['node']]
+            class_name = list(dep.keys())[0]
+            related_model = saved_models[dep[class_name]["node"]]
             data["%s_id" % class_name] = related_model.id
         return data
 
     def __init__(self, recipe, username, password, **kwargs):
 
         self.delete = False
-        if 'delete' in kwargs:
-            self.delete = True
+        if "delete" in kwargs:
+            self.delete = kwargs["delete"]
 
         # store username/password combination to read resources
         self.username = username
@@ -187,7 +193,9 @@
 
         try:
             # [] save the recipe to a tmp file
-            with NamedTemporaryFile(delete=False, suffix=".yaml", dir=TOSCA_RECIPES_DIR) as recipe_file:
+            with NamedTemporaryFile(
+                mode="w", delete=False, suffix=".yaml", dir=TOSCA_RECIPES_DIR
+            ) as recipe_file:
                 try:
                     recipe_file.write(self.recipe)
                     recipe_file.close()
@@ -203,49 +211,65 @@
             # [] compute requirements
             self.compute_dependencies(self.template, self.templates_by_model_name)
             # [] topsort requirements
-            self.ordered_models_name = self.topsort_dependencies(self.templates_by_model_name)
+            self.ordered_models_name = self.topsort_dependencies(
+                self.templates_by_model_name
+            )
             # [] topsort templates
-            self.ordered_models_template = self.get_ordered_models_template(self.ordered_models_name, self.templates_by_model_name)
+            self.ordered_models_template = self.get_ordered_models_template(
+                self.ordered_models_name, self.templates_by_model_name
+            )
 
             for recipe in self.ordered_models_template:
                 try:
                     # get properties from tosca
-                    if not 'properties' in recipe.templates[recipe.name]:
+                    if "properties" not in recipe.templates[recipe.name]:
                         data = {}
                     else:
-                        data = recipe.templates[recipe.name]['properties']
-                        if data == None:
+                        data = recipe.templates[recipe.name]["properties"]
+                        if data is None:
                             data = {}
                     # [] get model by class name
                     class_name = recipe.type.replace("tosca.nodes.", "")
 
                     # augemnt data with relations
-                    data = self.add_dependencies(data, recipe.requirements, self.saved_model_by_name)
+                    data = self.add_dependencies(
+                        data, recipe.requirements, self.saved_model_by_name
+                    )
 
-                    model = GRPCModelsAccessor.get_model_from_classname(class_name, data, self.username, self.password)
+                    model = GRPCModelsAccessor.get_model_from_classname(
+                        class_name, data, self.username, self.password
+                    )
                     # [] populate model with data
                     model = self.populate_model(model, data)
                     # [] check if the model has requirements
                     # [] if it has populate them
-                    model = self.populate_dependencies(model, recipe.requirements, self.saved_model_by_name)
+                    model = self.populate_dependencies(
+                        model, recipe.requirements, self.saved_model_by_name
+                    )
                     # [] save, update or delete
 
                     reference_only = False
-                    if 'must-exist' in data:
+                    if "must-exist" in data:
                         reference_only = True
 
                     if self.delete and not model.is_new and not reference_only:
-                        log.info("[XOS-Tosca] Deleting model %s[%s]" % (class_name, model.id))
+                        log.info(
+                            "[XOS-Tosca] Deleting model %s[%s]" % (class_name, model.id)
+                        )
                         model.delete()
                     elif not self.delete:
-                        log.info("[XOS-Tosca] Saving model %s[%s]" % (class_name, model.id))
+                        log.info(
+                            "[XOS-Tosca] Saving model %s[%s]" % (class_name, model.id)
+                        )
                         model.save()
 
-
                     self.saved_model_by_name[recipe.name] = model
-                except Exception, e:
-                    log.exception("[XOS-TOSCA] Failed to save model: %s [%s]" % (class_name, recipe.name))
-                    raise e
+
+                except GRPCModelsException as e:
+                    raise Exception(
+                        "[XOS-TOSCA] Failed to save or delete model %s [%s]: %s"
+                        % (class_name, recipe.name, str(e))
+                    )
 
         except ValidationError as e:
             if e.message:
@@ -254,17 +278,15 @@
                 exception_msg = TOSCA_Parser._translate_exception(str(e))
             raise Exception(exception_msg)
 
-        except _Rendezvous, e:
+        except _Rendezvous as e:
             try:
                 details = json.loads(e._state.details)
                 exception_msg = details["error"]
                 if "specific_error" in details:
-                    exception_msg = "%s: %s" % (exception_msg, details["specific_error"])
+                    exception_msg = "%s: %s" % (
+                        exception_msg,
+                        details["specific_error"],
+                    )
             except Exception:
                 exception_msg = e._state.details
             raise Exception(exception_msg)
-        except Exception, e:
-            log.exception(e)
-            raise Exception(e)
-
-
diff --git a/src/tosca/xtarget/tosca_keys.xtarget b/src/tosca/xtarget/tosca_keys.xtarget
index 9569061..6b73cb3 100644
--- a/src/tosca/xtarget/tosca_keys.xtarget
+++ b/src/tosca/xtarget/tosca_keys.xtarget
@@ -2,4 +2,5 @@
 {%- for m in proto.messages %}
     '{{ m.name }}': {{ xproto_fields_to_tosca_keys(m.fields + xproto_base_fields(m, proto.message_table), m) }},
 {%- endfor %}
-}
\ No newline at end of file
+}
+
diff --git a/src/web_server/__init__.py b/src/web_server/__init__.py
index d4e8062..ae374a7 100644
--- a/src/web_server/__init__.py
+++ b/src/web_server/__init__.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,4 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import absolute_import
 
+from .main import TOSCA_WebServer
+
+__all__ = [
+    'TOSCA_WebServer',
+]
diff --git a/src/web_server/main.py b/src/web_server/main.py
index 271b1b2..34a83f5 100644
--- a/src/web_server/main.py
+++ b/src/web_server/main.py
@@ -1,4 +1,3 @@
-
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,29 +12,34 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from xosconfig import Config
-from multistructlog import create_logger
-log = create_logger(Config().get('logging'))
+from __future__ import absolute_import, print_function
 
-from grpc_client.main import GRPC_Client
-from klein import Klein
-import os
-from tosca.parser import TOSCA_Parser
-from tosca.default import TOSCA_DEFS_DIR
 import json
+import os
 
-BANNER = """
-   _  ______  _____    __________  _____ _________ 
+from grpc_client import GRPC_Client
+from klein import Klein
+from multistructlog import create_logger
+from tosca.default import TOSCA_DEFS_DIR
+from tosca.parser import TOSCA_Parser
+from xosconfig import Config
+
+log = create_logger(Config().get("logging"))
+
+
+BANNER = r"""
+   _  ______  _____    __________  _____ _________
   | |/ / __ \/ ___/   /_  __/ __ \/ ___// ____/   |
   |   / / / /\__ \     / / / / / /\__ \/ /   / /| |
  /   / /_/ /___/ /    / / / /_/ /___/ / /___/ ___ |
 /_/|_\____//____/    /_/  \____//____/\____/_/  |_|
 """
 
+
 class TOSCA_WebServer:
 
     current_dir = os.path.dirname(os.path.realpath(__file__))
-    template_dir = os.path.join(current_dir, 'templates/')
+    template_dir = os.path.join(current_dir, "templates/")
 
     app = Klein()
 
@@ -59,48 +63,43 @@
             log.info("[XOS-TOSCA] Fatal Error: \n\n", failure=failure)
             return "Internal server error, please report this along with the failed recipe."
 
-    @app.route('/', methods=['GET'])
+    @app.route("/", methods=["GET"])
     def index(self, request):
         request.responseHeaders.addRawHeader(b"content-type", b"application/json")
-        tosca_defs = [f for f in os.listdir(TOSCA_DEFS_DIR) if not f.startswith('.')]
+        tosca_defs = [f for f in os.listdir(TOSCA_DEFS_DIR) if not f.startswith(".")]
 
         response = {}
         for d in tosca_defs:
-            name = d.replace('.yaml', '')
+            name = d.replace(".yaml", "")
             response[name] = "/custom_type/%s" % name
         return json.dumps(response)
 
     @app.route("/custom_type/<name>")
     def custom_type(self, request, name):
         request.responseHeaders.addRawHeader(b"content-type", b"text/plain")
-        custom_type = open(TOSCA_DEFS_DIR + '/' + name + '.yaml').read()
+        custom_type = open(TOSCA_DEFS_DIR + "/" + name + ".yaml").read()
         return custom_type
 
-    @app.route('/run', methods=['POST'])
+    @app.route("/run", methods=["POST"])
     def run(self, request):
-        recipe = request.content.read()
-        headers = request.getAllHeaders()
-        username = headers['xos-username']
-        password = headers['xos-password']
+        return self._handle_post(request, delete=False)
 
-        parser = TOSCA_Parser(recipe, username, password)
-        d = GRPC_Client().create_secure_client(username, password, parser)
-        tosca_execution = d.addCallback(self.execute_tosca)
-        tosca_execution.addErrback(self.errorCallback, request)
-        return d
-
-    @app.route('/delete', methods=['POST'])
+    @app.route("/delete", methods=["POST"])
     def delete(self, request):
-        recipe = request.content.read()
-        headers = request.getAllHeaders()
-        username = headers['xos-username']
-        password = headers['xos-password']
+        return self._handle_post(request, delete=True)
 
-        parser = TOSCA_Parser(recipe, username, password, delete=True)
+    def _handle_post(self, request, delete=False):
+
+        headers = request.getAllHeaders()
+        username = headers["xos-username"]
+        password = headers["xos-password"]
+        recipe = request.content.read()
+
+        parser = TOSCA_Parser(recipe, username, password, delete=delete)
         d = GRPC_Client().create_secure_client(username, password, parser)
         tosca_execution = d.addCallback(self.execute_tosca)
         tosca_execution.addErrback(self.errorCallback, request)
         return d
 
     def __init__(self):
-        self.app.run('0.0.0.0', '9102')
\ No newline at end of file
+        self.app.run("0.0.0.0", "9102")
diff --git a/src/xos-tosca-config-schema.yaml b/src/xos-tosca-config-schema.yaml
index db68a43..281bf77 100644
--- a/src/xos-tosca-config-schema.yaml
+++ b/src/xos-tosca-config-schema.yaml
@@ -1,4 +1,4 @@
-
+---
 # Copyright 2017-present Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,16 +13,15 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-
 map:
   name:
     type: str
-    required: True
+    required: true
   gprc_endpoint:
     type: str
-    required: True
+    required: true
   local_cert:
     type: str
-    required: True
+    required: true
   logging:
     type: any
diff --git a/src/xos-tosca.config.yaml b/src/xos-tosca.config.yaml
new file mode 100644
index 0000000..4231b3b
--- /dev/null
+++ b/src/xos-tosca.config.yaml
@@ -0,0 +1,14 @@
+---
+name: "xos-tosca"
+gprc_endpoint: "xos-core:30001"
+local_cert: ""
+logging:
+  version: 1
+  handlers:
+    console:
+      class: logging.StreamHandler
+  loggers:
+    'multistructlog':
+      handlers:
+        - console
+      level: ERROR