diff --git a/.travis.yml b/.travis.yml
index 52c5a9a..629bc5d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,10 +1,9 @@
 sudo: false
 language: python
 python:
-- 2.7
-- 3.6
 - 3.7
 - 3.8
+- 3.9
 install:
 - pip install -U setuptools
 - pip install -r requirements.txt #fix versions
diff --git a/docs/source/conf.py b/docs/source/conf.py
index 3e5973a..21f726b 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # skosprovider_getty documentation build configuration file, created by
 # sphinx-quickstart on Fri Sep 19 10:30:09 2014.
@@ -49,8 +48,8 @@
 master_doc = 'index'
 
 # General information about the project.
-project = u'skosprovider_getty'
-copyright = u'2014-2020, Flanders Heritage Agency'
+project = 'skosprovider_getty'
+copyright = '2014-2020, Flanders Heritage Agency'
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
@@ -202,8 +201,8 @@
 # (source start file, target name, title,
 #  author, documentclass [howto, manual, or own class]).
 latex_documents = [
-  ('index', 'skosprovider_getty.tex', u'skosprovider\\_getty Documentation',
-   u'Flanders Heritage Agency', 'manual'),
+  ('index', 'skosprovider_getty.tex', 'skosprovider\\_getty Documentation',
+   'Flanders Heritage Agency', 'manual'),
 ]
 
 # The name of an image file (relative to this directory) to place at the top of
@@ -232,8 +231,8 @@
 # One entry per manual page. List of tuples
 # (source start file, name, description, authors, manual section).
 man_pages = [
-    ('index', 'skosprovider_getty', u'skosprovider_getty Documentation',
-     [u'Flanders Heritage Agency'], 1)
+    ('index', 'skosprovider_getty', 'skosprovider_getty Documentation',
+     ['Flanders Heritage Agency'], 1)
 ]
 
 # If true, show URL addresses after external links.
@@ -246,8 +245,8 @@
 # (source start file, target name, title, author,
 #  dir menu entry, description, category)
 texinfo_documents = [
-  ('index', 'skosprovider_getty', u'skosprovider_getty Documentation',
-   u'Flanders Heritage Agency', 'skosprovider_getty', 'One line description of project.',
+  ('index', 'skosprovider_getty', 'skosprovider_getty Documentation',
+   'Flanders Heritage Agency', 'skosprovider_getty', 'One line description of project.',
    'Miscellaneous'),
 ]
 
diff --git a/examples/churches.py b/examples/churches.py
index 250ae8a..b7b298e 100755
--- a/examples/churches.py
+++ b/examples/churches.py
@@ -1,5 +1,4 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 '''
 This script demonstrates using the AATProvider to get the concept of
 Churches.
@@ -9,20 +8,20 @@
 
 aat = AATProvider(metadata={'id': 'AAT'})
 
-churches = aat.get_by_id(300007466)
+churches = aat.get_by_id('300007466')
 
-lang = ['en', 'nl', 'es', 'de', 'fr']
+langs = ['en', 'nl', 'es', 'de', 'fr']
 
 print('Label per language')
 print('------------------')
-for l in lang:
-    label = churches.label(l)
-    print(l + ' --> ' + label.language + ': ' + label.label + ' [' + label.type + ']')
+for lang in langs:
+    label = churches.label(lang)
+    print(lang + ' --> ' + label.language + ': ' + label.label + ' [' + label.type + ']')
 
 print('All Labels')
 print('----------')
-for l in churches.labels:
-   print(l.language + ': ' + l.label + ' [' + l.type + ']')
+for lang in churches.labels:
+    print(lang.language + ': ' + lang.label + ' [' + lang.type + ']')
 
 print('All Notes')
 print('---------')
diff --git a/examples/collect_subclasses.py b/examples/collect_subclasses.py
index 64246d5..9e09415 100644
--- a/examples/collect_subclasses.py
+++ b/examples/collect_subclasses.py
@@ -1,5 +1,4 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 '''
 This script demonstrates retrieving subclasses for a certain class.
 '''
diff --git a/examples/expand.py b/examples/expand.py
index cf241a1..a96c836 100755
--- a/examples/expand.py
+++ b/examples/expand.py
@@ -1,5 +1,4 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 '''
 This script demonstrates using the AATProvider to expand a collection
 '''
@@ -11,4 +10,4 @@
 print('Results')
 print('------')
 for result in results:
-    print(result)
\ No newline at end of file
+    print(result)
diff --git a/examples/find.py b/examples/find.py
index 761df18..53f1850 100755
--- a/examples/find.py
+++ b/examples/find.py
@@ -1,15 +1,20 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 '''
-This script demonstrates using the AATProvider to find the concepts that are a member of a collection with 'church' in their label
+This script demonstrates using the AATProvider to find the concepts that are a member of
+a collection with 'church' in their label
 '''
 
 from skosprovider_getty.providers import AATProvider
 
-results = AATProvider({'id': 'AAT', 'default_language': 'nl'}).find({'label': 'church', 'type': 'concept', 'collection': {'id': '300007466', 'depth': 'all'}})
+results = AATProvider({'id': 'AAT', 'default_language': 'nl'}).find(
+    {
+        'label': 'church',
+        'type': 'concept',
+        'collection': {'id': '300007466', 'depth': 'all'}
+    }
+)
 
 print('Results')
 print('------')
 for result in results:
     print(result)
-
diff --git a/examples/flanders.py b/examples/flanders.py
index 8afc949..d14ddcc 100755
--- a/examples/flanders.py
+++ b/examples/flanders.py
@@ -1,5 +1,4 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 '''
 This script demonstrates using the TGNProvider to get the concept of
 Flanders.
@@ -11,18 +10,18 @@
 
 flanders = aat.get_by_id(7018236)
 
-lang = ['en', 'nl', 'es', 'de', 'fr']
+langs = ['en', 'nl', 'es', 'de', 'fr']
 
 print('Label per language')
 print('------------------')
-for l in lang:
-    label = flanders.label(l)
-    print(l + ' --> ' + label.language + ': ' + label.label + ' [' + label.type + ']')
+for lang in langs:
+    label = flanders.label(lang)
+    print(lang + ' --> ' + label.language + ': ' + label.label + ' [' + label.type + ']')
 
 print('Labels')
 print('------')
-for l in flanders.labels:
-   print(l.language + ': ' + l.label + ' [' + l.type + ']')
+for lang in flanders.labels:
+    print(lang.language + ': ' + lang.label + ' [' + lang.type + ']')
 
 print('Notes')
 print('-----')
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 9ac277d..adab7ba 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -4,8 +4,8 @@
 # Testing
 pytest==4.6.9 ; python_version < '3.0'
 pytest==5.3.5 ; python_version >= '3.0'
-pytest-cov==2.8.1
-coveralls==1.11.1
+pytest-cov==3.0.0
+coveralls==3.3.1
 
 # Documentation
 Sphinx==1.8.5 ; python_version < '3.5'
diff --git a/requirements.txt b/requirements.txt
index c9538a7..279fdba 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
-requests==2.24.0
-skosprovider==0.7.1
+requests==2.26.0
+skosprovider==1.0.0
 #-e git+https://github.com/koenedaele/skosprovider.git@DEV_0.7.0#egg=skosprovider
-rdflib==5.0.0
+rdflib==6.0.2
diff --git a/setup.py b/setup.py
index 02ecfe4..5c35b4d 100644
--- a/setup.py
+++ b/setup.py
@@ -1,7 +1,7 @@
 import os
 
 try:
-    from setuptools import setup, find_packages
+    from setuptools import setup
 except ImportError:
     from distutils.core import setup
 
diff --git a/skosprovider_getty/providers.py b/skosprovider_getty/providers.py
index 45ff0b0..b5e3163 100644
--- a/skosprovider_getty/providers.py
+++ b/skosprovider_getty/providers.py
@@ -1,31 +1,29 @@
-# -*- coding: utf-8 -*-
 '''
 This module contains classes that implement
 :class:`skosprovider.providers.VocabularyProvider` against the LOD version of
 the Getty Vocabularies (AAT, TGN and ULAN).
 
 .. note::
-    | At initialisation, the Getty providers will search which gvp-classes of the gvp-ontology are a subclass of skos-classes.
+    | At initialisation, the Getty providers will search which gvp-classes of the
+    gvp-ontology are a subclass of skos-classes.
     | This can cause a time delay of several seconds at startup.
 
 '''
 
-import requests
-import warnings
 import logging
+import warnings
 
+import requests
 from language_tags import tags
-from requests.exceptions import ConnectionError, Timeout
-from skosprovider.exceptions import ProviderUnavailableException
 from skosprovider.providers import VocabularyProvider
-from skosprovider_getty.utils import (
-    uri_to_id, uri_to_graph,
-    conceptscheme_from_uri,
-    things_from_graph,
-    SubClassCollector,
-    GVP,
-    do_get_request
-)
+
+from skosprovider_getty.utils import GVP
+from skosprovider_getty.utils import SubClassCollector
+from skosprovider_getty.utils import conceptscheme_from_uri
+from skosprovider_getty.utils import do_get_request
+from skosprovider_getty.utils import things_from_graph
+from skosprovider_getty.utils import uri_to_graph
+from skosprovider_getty.utils import uri_to_id
 
 log = logging.getLogger(__name__)
 
@@ -49,7 +47,7 @@ def __init__(self, metadata, **kwargs):
             * The :class:`skosprovider_getty.providers.AATProvider`
                 is the default :class:`skosprovider_getty.providers.GettyProvider`
         """
-        if not 'default_language' in metadata:
+        if 'default_language' not in metadata:
             metadata['default_language'] = 'en'
         if 'subject' not in metadata:
             metadata['subject'] = []
@@ -91,9 +89,9 @@ def get_by_id(self, id, change_notes=False):
         :return: corresponding :class:`skosprovider.skos.Concept` or :class:`skosprovider.skos.Concept`.
             Returns None if non-existing id
         """
-        graph = uri_to_graph('%s/%s.rdf' % (self.url, id), session=self.session)
+        graph = uri_to_graph(f'{self.url}/{id}.rdf', session=self.session)
         if graph is False:
-            log.debug('Failed to retrieve data for %s/%s.rdf' % (self.url, id))
+            log.debug(f'Failed to retrieve data for {self.url}/{id}.rdf')
             return False
         # get the concept
         things = things_from_graph(
@@ -107,7 +105,6 @@ def get_by_id(self, id, change_notes=False):
         c = things[0]
         return c
 
-
     def get_by_uri(self, uri, change_notes=False):
         """ Get a :class:`skosprovider.skos.Concept` or :class:`skosprovider.skos.Collection` by uri
 
@@ -187,12 +184,12 @@ def find(self, query, **kwargs):
             type_c = query['type']
         if type_c not in ('all', 'concept', 'collection'):
             raise ValueError("type: only the following values are allowed: 'all', 'concept', 'collection'")
-        #Collection to search in (optional)
+        # Collection to search in (optional)
         coll_id = None
         coll_depth = None
         if 'collection' in query:
             coll = query['collection']
-            if not 'id' in coll:
+            if 'id' not in coll:
                 raise ValueError("collection: 'id' is required key if a collection-dictionary is given")
             coll_id = coll['id']
             coll_depth = 'members'
@@ -201,7 +198,7 @@ def find(self, query, **kwargs):
             if coll_depth not in ('members', 'all'):
                 raise ValueError(
                     "collection - 'depth': only the following values are allowed: 'members', 'all'")
-        #Matches (optional)
+        # Matches (optional)
         match_uri = None
         match_pred = 'skos:mappingRelation'
         if 'matches' in query:
@@ -214,7 +211,7 @@ def find(self, query, **kwargs):
             if match_type:
                 match_pred = 'skos:%sMatch' % match_type
 
-        #build sparql query
+        # build sparql query
         coll_x = ""
         if coll_id is not None and coll_depth == 'all':
             coll_x = "gvp:broaderExtended " + self.vocab_id + ":" + coll_id + ";"
@@ -223,7 +220,7 @@ def find(self, query, **kwargs):
 
         match_values = ""
         if match_uri is not None:
-            match_values = "%s <%s>;" % (match_pred, match_uri)
+            match_values = f"{match_pred} <{match_uri}>;"
 
         type_values = "((?Type = skos:Concept) || (?Type = skos:Collection))"
         if type_c == 'concept':
@@ -231,17 +228,17 @@ def find(self, query, **kwargs):
         elif type_c == 'collection':
             type_values = "(?Type = skos:Collection)"
         query = """
-            SELECT ?Subject ?Term ?Type ?Id (lang(?Term) as ?Lang) {
-            ?Subject rdf:type ?Type; dc:identifier ?Id; skos:inScheme %s:; %s%s%s.
-                            OPTIONAL {
-                  {?Subject xl:prefLabel [skosxl:literalForm ?Term]}
-                          }
-            FILTER(%s)
-            }""" % (
+            SELECT ?Subject ?Term ?Type ?Id (lang(?Term) as ?Lang) {{
+            ?Subject rdf:type ?Type; dc:identifier ?Id; skos:inScheme {}:; {}{}{}.
+                            OPTIONAL {{
+                  {{?Subject xl:prefLabel [skosxl:literalForm ?Term]}}
+                          }}
+            FILTER({})
+            }}""".format(
                 self.vocab_id,
                 self._build_keywords(label), coll_x, match_values,
                 type_values)
-        ret= self._get_answer(query, **kwargs)
+        ret = self._get_answer(query, **kwargs)
         language = self._get_language(**kwargs)
         sort = self._get_sort(**kwargs)
         sort_order = self._get_sort_order(**kwargs)
@@ -281,11 +278,11 @@ def _get_answer(self, query, **kwargs):
             else:
                 label = "<not available>"
             item = {
-            'id': result["Id"]["value"],
-            'uri': uri,
-            'type': result["Type"]["value"].rsplit('#', 1)[1].lower(),
-            'label': label,
-            'lang': result["Lang"]["value"]
+                'id': result["Id"]["value"],
+                'uri': uri,
+                'type': result["Type"]["value"].rsplit('#', 1)[1].lower(),
+                'label': label,
+                'lang': result["Lang"]["value"]
             }
 
             if uri not in d:
@@ -294,13 +291,15 @@ def _get_answer(self, query, **kwargs):
                 pass
             elif tags.tag(item['lang']).format == tags.tag(self._get_language(**kwargs)).format:
                 d[uri] = item
-            elif tags.tag(item['lang']).language and (tags.tag(item['lang']).language.format == tags.tag(self._get_language()).language.format):
+            elif (
+                    tags.tag(item['lang']).language and (
+                    tags.tag(item['lang']).language.format == tags.tag(self._get_language()).language.format)
+            ):
                 d[uri] = item
             elif tags.tag(item['lang']).format == tags.tag('en').format:
                 d[uri] = item
         return list(d.values())
 
-
     def _get_top(self, type='All', **kwargs):
         """ Returns all top-level facets. The returned values depend on the given type:
             Concept or All (Concepts and Collections). Default All is used.
@@ -309,21 +308,21 @@ def _get_top(self, type='All', **kwargs):
         :return: A :class:`lst` of concepts (and collections).
         """
 
-        if type == "concepts" :
+        if type == "concepts":
             type_values = "(?Type = skos:Concept)"
         else:
             type_values = "((?Type = skos:Concept) || (?Type = skos:Collection))"
 
         query = """SELECT ?Subject ?Id ?Type ?Term (lang(?Term) as ?Lang)
-                {
+                {{
                 ?Subject a gvp:Facet; rdf:type ?Type;
-                 dc:identifier ?Id; skos:inScheme %s:;.
-                 OPTIONAL {
-                  {?Subject xl:prefLabel [skosxl:literalForm ?Term]}
-                          }
-                FILTER (%s)
-                }""" % (self.vocab_id, type_values)
-        ret= self._get_answer(query, **kwargs)
+                 dc:identifier ?Id; skos:inScheme {}:;.
+                 OPTIONAL {{
+                  {{?Subject xl:prefLabel [skosxl:literalForm ?Term]}}
+                          }}
+                FILTER ({})
+                }}""".format(self.vocab_id, type_values)
+        ret = self._get_answer(query, **kwargs)
         language = self._get_language(**kwargs)
         sort = self._get_sort(**kwargs)
         sort_order = self._get_sort_order(**kwargs)
@@ -336,7 +335,6 @@ def get_top_concepts(self, **kwargs):
         """
         return self._get_top("concepts", **kwargs)
 
-
     def get_top_display(self, **kwargs):
         """  Returns all concepts or collections that form the top-level of a display hierarchy.
 
@@ -354,16 +352,16 @@ def get_children_display(self, id, **kwargs):
         type_values = "((?Type = skos:Concept) || (?Type = skos:Collection))"
 
         query = """SELECT ?Subject ?Id ?Type ?Term (lang(?Term) as ?Lang)
-                {
+                {{
                 ?Subject rdf:type ?Type;
-                dc:identifier ?Id; skos:inScheme %s:; gvp:%s %s:%s;.
-                OPTIONAL {
-                  {?Subject xl:prefLabel [skosxl:literalForm ?Term]}
-                          }
-                FILTER(%s)
-                }""" % (self.vocab_id, broader, self.vocab_id, id, type_values)
-
-        ret= self._get_answer(query, **kwargs)
+                dc:identifier ?Id; skos:inScheme {}:; gvp:{} {}:{};.
+                OPTIONAL {{
+                  {{?Subject xl:prefLabel [skosxl:literalForm ?Term]}}
+                          }}
+                FILTER({})
+                }}""".format(self.vocab_id, broader, self.vocab_id, id, type_values)
+
+        ret = self._get_answer(query, **kwargs)
         language = self._get_language(**kwargs)
         sort = self._get_sort(**kwargs)
         sort_order = self._get_sort_order(**kwargs)
@@ -378,19 +376,19 @@ def expand(self, id):
         :returns: A :class:`lst` of id's. Returns false if the input id does not exists
         """
 
-        query = """SELECT DISTINCT ?Id{
-                {
-                ?Subject dc:identifier ?Id; skos:inScheme %s:; gvp:broaderExtended %s;.
-                }
+        query = """SELECT DISTINCT ?Id{{
+                {{
+                ?Subject dc:identifier ?Id; skos:inScheme {}:; gvp:broaderExtended {};.
+                }}
                 UNION
-                {
-                VALUES ?Id {'%s'}
-                ?Subject dc:identifier ?Id; skos:inScheme %s:; rdf:type skos:Concept.
-                }
-                }
-                """ % (self.vocab_id, self.vocab_id + ":" + id, id, self.vocab_id)
-
-        print (query)
+                {{
+                VALUES ?Id {{'{}'}}
+                ?Subject dc:identifier ?Id; skos:inScheme {}:; rdf:type skos:Concept.
+                }}
+                }}
+                """.format(self.vocab_id, self.vocab_id + ":" + id, id, self.vocab_id)
+
+        print(query)
         request = self.base_url + "sparql.json"
         res = do_get_request(request, self.session, params={'query': query})
         r = res.json()
@@ -417,7 +415,7 @@ def _sort(self, items, sort, language='en', reverse=False):
         if sort is None:
             sort = 'id'
         if sort == 'sortlabel':
-            sort='label'
+            sort = 'label'
         items.sort(key=lambda item: item[sort], reverse=reverse)
         return items
 
diff --git a/skosprovider_getty/utils.py b/skosprovider_getty/utils.py
index 5d39d3f..2ea7bc3 100644
--- a/skosprovider_getty/utils.py
+++ b/skosprovider_getty/utils.py
@@ -1,31 +1,33 @@
-# -*- coding: utf-8 -*-
-
 '''
 This module contains utility functions for :mod:`skosprovider_getty`.
 '''
-import requests
+import logging
+
 import rdflib
+import requests
 from rdflib.graph import Graph
+from rdflib.namespace import DC
+from rdflib.namespace import RDF
+from rdflib.namespace import RDFS
+from rdflib.namespace import SKOS
 from rdflib.term import URIRef
-from requests.exceptions import ConnectionError, Timeout
+from requests.exceptions import ConnectionError
+from requests.exceptions import Timeout
 from skosprovider.exceptions import ProviderUnavailableException
+from skosprovider.skos import Collection
+from skosprovider.skos import Concept
+from skosprovider.skos import ConceptScheme
+from skosprovider.skos import Label
+from skosprovider.skos import Note
 
-from skosprovider.skos import (
-    Concept,
-    Collection,
-    Label,
-    Note,
-    ConceptScheme)
-
-import logging
 log = logging.getLogger(__name__)
 
-from rdflib.namespace import RDFS, RDF, SKOS, DC
 
 PROV = rdflib.Namespace('http://www.w3.org/ns/prov#')
 ISO = rdflib.Namespace('http://purl.org/iso25964/skos-thes#')
 GVP = rdflib.Namespace('http://vocab.getty.edu/ontology#')
 
+
 def conceptscheme_from_uri(conceptscheme_uri, **kwargs):
     '''
     Read a SKOS Conceptscheme from a :term:`URI`
@@ -75,14 +77,14 @@ def things_from_graph(graph, subclasses, conceptscheme, **kwargs):
         con = Concept(
             uri_to_id(uri),
             uri=uri,
-            concept_scheme = conceptscheme,
-            labels = _create_from_subject_typelist(graph, sub, valid_label_types),
-            notes = _create_from_subject_typelist(graph, sub, hierarchy_notetypes(Note.valid_types)),
-            sources = [],
-            broader = _create_from_subject_predicate(graph, sub, SKOS.broader),
-            narrower = _create_from_subject_predicate(graph, sub, SKOS.narrower),
-            related = _create_from_subject_predicate(graph, sub, SKOS.related),
-            subordinate_arrays = _create_from_subject_predicate(graph, sub, ISO.subordinateArray),
+            concept_scheme=conceptscheme,
+            labels=_create_from_subject_typelist(graph, sub, valid_label_types),
+            notes=_create_from_subject_typelist(graph, sub, hierarchy_notetypes(Note.valid_types)),
+            sources=[],
+            broader=_create_from_subject_predicate(graph, sub, SKOS.broader),
+            narrower=_create_from_subject_predicate(graph, sub, SKOS.narrower),
+            related=_create_from_subject_predicate(graph, sub, SKOS.related),
+            subordinate_arrays=_create_from_subject_predicate(graph, sub, ISO.subordinateArray),
             matches=matches
         )
         clist.append(con)
@@ -92,12 +94,12 @@ def things_from_graph(graph, subclasses, conceptscheme, **kwargs):
         col = Collection(
             uri_to_id(uri),
             uri=uri,
-            concept_scheme = conceptscheme,
-            labels = _create_from_subject_typelist(graph, sub, valid_label_types),
-            notes = _create_from_subject_typelist(graph, sub, hierarchy_notetypes(Note.valid_types)),
-            sources = [],
-            members = _create_from_subject_predicate(graph, sub, SKOS.member),
-            superordinates = _get_super_ordinates(conceptscheme, sub, session=s)
+            concept_scheme=conceptscheme,
+            labels=_create_from_subject_typelist(graph, sub, valid_label_types),
+            notes=_create_from_subject_typelist(graph, sub, hierarchy_notetypes(Note.valid_types)),
+            sources=[],
+            members=_create_from_subject_predicate(graph, sub, SKOS.member),
+            superordinates=_get_super_ordinates(conceptscheme, sub, session=s)
         )
         clist.append(col)
 
@@ -108,7 +110,7 @@ def _create_from_subject_typelist(graph, subject, typelist):
     list = []
     note_uris = []
     for p in typelist:
-        term = SKOS.term(p)
+        term = SKOS._NS.term(p)
         list.extend(_create_from_subject_predicate(graph, subject, term, note_uris))
     return list
 
@@ -116,8 +118,8 @@ def _create_from_subject_typelist(graph, subject, typelist):
 def _get_super_ordinates(conceptscheme, sub, **kwargs):
     ret = []
     s = kwargs.get('session', requests.Session())
-    query = """PREFIX ns:<%s>
-    SELECT * WHERE {?s iso-thes:subordinateArray ns:%s}""" % (conceptscheme.uri, uri_to_id(sub))
+    query = """PREFIX ns:<{}>
+    SELECT * WHERE {{?s iso-thes:subordinateArray ns:{}}}""".format(conceptscheme.uri, uri_to_id(sub))
     url = conceptscheme.uri.strip('/').rsplit('/', 1)[0] + "/sparql.json"
     res = do_get_request(url, s, params={'query': query})
     r = res.json()
@@ -150,18 +152,18 @@ def _create_label(literal, type):
     if language is None:
         language = 'und'
     try:
-        l = Label(literal.toPython(), type, language)
-    except ValueError as e:
+        lang = Label(literal.toPython(), type, language)
+    except ValueError:
         log.warn('Received a label with an invalid language tag: %s.', language)
-        l = Label(literal.toPython(), type, 'und')
-    return l
+        lang = Label(literal.toPython(), type, 'und')
+    return lang
 
 
 def _create_note(graph, uri, type, change_notes=False):
     if not change_notes and '/rev/' in uri:
         return None
     else:
-        note = u''
+        note = ''
         language = 'en'
 
         # http://vocab.getty.edu/aat/scopeNote
@@ -184,6 +186,7 @@ class SubClassCollector:
     '''
     A utility class to collect all the subclasses of a certain Class from an ontology file.
     '''
+
     def __init__(self, namespace):
         self.ontology_graphs = {}
         self.namespace = namespace
@@ -232,12 +235,12 @@ def collect_subclasses(self, clazz):
         if self.namespace not in self.ontology_graphs:
             try:
                 graph = rdflib.Graph()
-                result = graph.parse(str(self.namespace), format="application/rdf+xml")
+                graph.parse(str(self.namespace), format="application/rdf+xml")
                 self.ontology_graphs[self.namespace] = graph
-            except: # pragma: no cover
+            except:  # pragma: no cover # noqa: E722
                 self.ontology_graphs[self.namespace] = None
         g = self.ontology_graphs[self.namespace]
-        if not g is None:
+        if g is not None:
             for sub, pred, obj in g.triples((None, RDFS.subClassOf, None)):
                 self._is_subclass_of(sub, clazz)
         return self.subclasses[clazz]
@@ -249,12 +252,12 @@ def _is_subclass_of(self, subject, clazz):
         if namespace not in self.ontology_graphs:
             try:
                 graph = rdflib.Graph()
-                result = graph.parse(str(namespace), format="application/rdf+xml")
+                graph.parse(str(namespace), format="application/rdf+xml")
                 self.ontology_graphs[namespace] = graph
-            except: # pragma: no cover
+            except:  # pragma: no cover # noqa: E722
                 self.ontology_graphs[namespace] = None
         g = self.ontology_graphs[namespace]
-        if not g is None:
+        if g is not None:
             for sub, pred, obj in g.triples((subject, RDFS.subClassOf, None)):
                 if obj in self.subclasses[clazz]:
                     self.subclasses[clazz].append(subject)
@@ -297,7 +300,8 @@ def uri_to_graph(uri, **kwargs):
     res = do_get_request(uri, s)
     if res.status_code == 404:
         return False
-    graph.parse(data=res.content)
+    content_type = res.headers['Content-Type'].split(';')[0]
+    graph.parse(data=res.content, format=content_type)
     return graph
 
 
@@ -307,11 +311,12 @@ def do_get_request(url, session=None, headers=None, params=None):
     try:
         res = session.get(url, headers=headers, params=params)
     except ConnectionError:
-        raise ProviderUnavailableException("Request could not be executed due to connection issues- Request: %s" % (url,))
-    except Timeout: # pragma: no cover
-        raise ProviderUnavailableException("Request could not be executed due to timeout - Request: %s" % (url,))
+        raise ProviderUnavailableException(f"Request could not be executed due to connection issues- Request: {url}")
+    except Timeout:  # pragma: no cover
+        raise ProviderUnavailableException(f"Request could not be executed due to timeout - Request: {url}")
     if res.status_code >= 500:
-        raise ProviderUnavailableException("Request could not be executed due to server issues - Request: %s. Response: %s." % (url, res.content))
+        raise ProviderUnavailableException(
+            f"Request could not be executed due to server issues - Request: {url}. Response: {res.content}.")
     if not res.encoding:
         res.encoding = 'utf-8'
     return res
diff --git a/tests/test_providers.py b/tests/test_providers.py
index e3bdb44..4a0fb7c 100644
--- a/tests/test_providers.py
+++ b/tests/test_providers.py
@@ -1,18 +1,14 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
-import pytest
-from rdflib.namespace import SKOS, Namespace
+import unittest
 
+import pytest
+import requests
 from skosprovider.exceptions import ProviderUnavailableException
 
-from skosprovider_getty.providers import (
-    AATProvider,
-    TGNProvider,
-    ULANProvider,
-    GettyProvider
-)
-import unittest
-from skosprovider_getty.utils import SubClassCollector
+from skosprovider_getty.providers import AATProvider
+from skosprovider_getty.providers import GettyProvider
+from skosprovider_getty.providers import TGNProvider
+from skosprovider_getty.providers import ULANProvider
 
 global clazzes, ontologies
 clazzes = []
@@ -22,7 +18,6 @@
 class GettyProviderTests(unittest.TestCase):
 
     def test_set_custom_session(self):
-        import requests
         sess = requests.Session()
         provider = AATProvider({'id': 'AAT'}, session=sess)
         self.assertEqual(sess, provider.session)
@@ -36,7 +31,7 @@ def test_allowed_instance_scopes(self):
     def test_override_instance_scopes(self):
         provider = AATProvider(
             {'id': 'AAT'},
-            allowed_instance_scopes = ['single']
+            allowed_instance_scopes=['single']
         )
         assert provider.allowed_instance_scopes == ['single']
 
@@ -69,14 +64,14 @@ def test_get_by_id_concept(self):
         self.assertEqual(concept['type'], 'concept')
         self.assertIsInstance(concept['labels'], list)
 
-        preflabels = [{'nl': 'kerken'}, {'de': u'Kirche (Gebäude)'}]
+        preflabels = [{'nl': 'kerken'}, {'de': 'Kirche (Gebäude)'}]
         preflabels_conc = [{label.language: label.label} for label in concept['labels']
                            if label.type == 'prefLabel']
         self.assertGreater(len(preflabels_conc), 0)
         for label in preflabels:
             self.assertIn(label, preflabels_conc)
 
-        altlabels = [{u'nl': 'kerk'}, {u'de': u'kirchen (Gebäude)'}]
+        altlabels = [{'nl': 'kerk'}, {'de': 'kirchen (Gebäude)'}]
         altlabels_conc = [{label.language: label.label} for label in concept['labels']
                           if label.type == 'altLabel']
         self.assertGreater(len(altlabels_conc), 0)
@@ -86,8 +81,10 @@ def test_get_by_id_concept(self):
         self.assertGreater(len(concept['notes']), 0)
 
         self.assertEqual(concept['id'], '300007466')
-        #todo gvp:broader is not a subproperty of skos:broader anymore. This is the reason why there are no broader elements anymore belonging to the Concept...to be decided what to do...
-        #self.assertEqual(concept['broader'][0], '300007391')
+        # todo gvp:broader is not a subproperty of skos:broader anymore. This is the
+        #  reason why there are no broader elements anymore belonging to the Concept...
+        #  to be decided what to do...
+        # self.assertEqual(concept['broader'][0], '300007391')
         self.assertIn('300312247', concept['related'])
 
     def test_get_by_id_collection(self):
@@ -95,8 +92,9 @@ def test_get_by_id_collection(self):
         assert collection is not False
         assert collection.uri == 'http://vocab.getty.edu/aat/300007473'
         assert collection.type == 'collection'
-        assert u'<kerken naar vorm>' in [label.label for label in collection.labels if label.language == 'nl' and label.type == 'prefLabel']
-        assert len(collection.notes) ==  0
+        assert '<kerken naar vorm>' in [
+            label.label for label in collection.labels if label.language == 'nl' and label.type == 'prefLabel']
+        assert len(collection.notes) == 0
 
     def test_get_by_id_invalid(self):
         concept = AATProvider({'id': 'AAT'}).get_by_id('123')
@@ -114,7 +112,7 @@ def test_get_by_id_subOrdinateArrays(self):
         concept = concept.__dict__
         self.assertEqual(concept['id'], '300138225')
         self.assertIn('300138225-array', concept['subordinate_arrays'])
-        #300126352
+        # 300126352
 
     def test_get_by_uri(self):
         # Default GettyProvider is an AAT provider
@@ -134,7 +132,7 @@ def test_get_by_id_tgn(self):
         concept = TGNProvider({'id': 'TGN'}).get_by_id('1000063')
         concept = concept.__dict__
         self.assertEqual(concept['uri'], 'http://vocab.getty.edu/tgn/1000063')
-        self.assertIn(u'België', [label.label for label in concept['labels']
+        self.assertIn('België', [label.label for label in concept['labels']
                                  if label.language == 'nl' and label.type == 'prefLabel'])
 
     def test_get_all(self):
@@ -149,11 +147,11 @@ def test_get_top_display(self):
         keys_first_display = top_TGN_display[0].keys()
         for key in ['id', 'type', 'label', 'uri']:
             self.assertIn(key, keys_first_display)
-        self.assertIn(u'World', [label['label'] for label in top_TGN_display])
+        self.assertIn('World', [label['label'] for label in top_TGN_display])
         top_AAT_display = AATProvider({'id': 'AAT', 'default_language': 'nl'}).get_top_display()
         self.assertIsInstance(top_AAT_display, list)
         self.assertGreater(len(top_AAT_display), 0)
-        self.assertIn(u'Facet Stijlen en perioden', [label['label'] for label in top_AAT_display])
+        self.assertIn('Facet Stijlen en perioden', [label['label'] for label in top_AAT_display])
 
     def test_get_top_concepts(self):
         kwargs = {'language': 'nl'}
@@ -163,13 +161,14 @@ def test_get_top_concepts(self):
 
     def test_get_childeren_display(self):
         kwargs = {'language': 'nl'}
-        childeren_tgn_belgie = TGNProvider({'id': 'TGN', 'default_language': 'nl'}).get_children_display('1000063', **kwargs)
+        childeren_tgn_belgie = TGNProvider({'id': 'TGN', 'default_language': 'nl'}
+                                           ).get_children_display('1000063', **kwargs)
         self.assertIsInstance(childeren_tgn_belgie, list)
         self.assertGreater(len(childeren_tgn_belgie), 0)
         keys_first_display = childeren_tgn_belgie[0].keys()
         for key in ['id', 'type', 'label', 'uri']:
             self.assertIn(key, keys_first_display)
-        self.assertIn(u'Brussels Hoofdstedelijk Gewest', [label['label'] for label in childeren_tgn_belgie])
+        self.assertIn('Brussels Hoofdstedelijk Gewest', [label['label'] for label in childeren_tgn_belgie])
 
     def test_expand(self):
         all_childeren_churches = AATProvider({'id': 'AAT'}).expand('300007466')
@@ -192,16 +191,20 @@ def test_find_without_label(self):
         self.assertIsInstance(r, list)
 
     def test_find_wrong_type(self):
-        self.assertRaises(ValueError, AATProvider({'id': 'AAT'}).find, {'type': 'collectie', 'collection': {'id': '300007466', 'depth': 'all'}})
+        self.assertRaises(ValueError, AATProvider({'id': 'AAT'}).find, {
+            'type': 'collectie', 'collection': {'id': '300007466', 'depth': 'all'}})
 
     def test_find_no_collection_id(self):
-        self.assertRaises(ValueError, AATProvider({'id': 'AAT'}).find, {'type': 'collection', 'collection': {'depth': 'all'}})
+        self.assertRaises(ValueError, AATProvider({'id': 'AAT'}).find, {
+            'type': 'collection', 'collection': {'depth': 'all'}})
 
     def test_find_wrong_collection_depth(self):
-        self.assertRaises(ValueError, AATProvider({'id': 'AAT'}).find, {'type': 'concept', 'collection': {'id': '300007466', 'depth': 'allemaal'}})
+        self.assertRaises(ValueError, AATProvider({'id': 'AAT'}).find, {
+            'type': 'concept', 'collection': {'id': '300007466', 'depth': 'allemaal'}})
 
     def test_find_concepts_in_collection(self):
-        r = AATProvider({'id': 'AAT'}).find({'label': 'church', 'type': 'concept', 'collection': {'id': '300007466', 'depth': 'all'}})
+        r = AATProvider({'id': 'AAT'}).find({'label': 'church', 'type': 'concept',
+                                             'collection': {'id': '300007466', 'depth': 'all'}})
         self.assertIsInstance(r, list)
         self.assertGreater(len(r), 0)
         for res in r:
@@ -215,14 +218,16 @@ def test_find_multiple_keywords(self):
             assert res['type'] == 'concept'
 
     def test_find_member_concepts_in_collection(self):
-        r = AATProvider({'id': 'AAT'}).find({'label': 'church', 'type': 'concept', 'collection': {'id': '300007494', 'depth': 'members'}})
+        r = AATProvider({'id': 'AAT'}).find({'label': 'church', 'type': 'concept',
+                                             'collection': {'id': '300007494', 'depth': 'members'}})
         self.assertIsInstance(r, list)
         self.assertGreater(len(r), 0)
         for res in r:
             assert res['type'] == 'concept'
 
     def test_find_collections_in_collection(self):
-        r = AATProvider({'id': 'AAT'}).find({'label': 'church', 'type': 'collection', 'collection': {'id': '300007466', 'depth': 'all'}})
+        r = AATProvider({'id': 'AAT'}).find({'label': 'church', 'type': 'collection',
+                                             'collection': {'id': '300007466', 'depth': 'all'}})
         assert len(r) > 0
         for res in r:
             assert res['type'] == 'collection'
@@ -270,8 +275,9 @@ def test_find_concepts_kerk(self):
             assert res['type'] == 'concept'
 
     def test_find_member_collections_in_collection(self):
-        r = AATProvider({'id': 'AAT'}).find({'label': 'church', 'type': 'collection', 'collection': {'id': '300007466', 'depth': 'members'}})
-        assert len (r) > 0
+        r = AATProvider({'id': 'AAT'}).find({'label': 'church', 'type': 'collection',
+                                             'collection': {'id': '300007466', 'depth': 'members'}})
+        assert len(r) > 0
         for res in r:
             assert res['type'] == 'collection'
 
@@ -282,14 +288,15 @@ def test_find_matches(self):
         assert r[0]['uri'] == 'http://vocab.getty.edu/aat/300191778'
 
     def test_find_closematches(self):
-        r = AATProvider({'id': 'AAT'}).find({'matches': {'uri': 'http://id.loc.gov/authorities/subjects/sh85123119', 'type': 'close'}})
+        r = AATProvider({'id': 'AAT'}).find(
+            {'matches': {'uri': 'http://id.loc.gov/authorities/subjects/sh85123119', 'type': 'close'}})
         assert len(r) == 1
         assert r[0]['type'] == 'concept'
         assert r[0]['uri'] == 'http://vocab.getty.edu/aat/300191778'
 
     def test_find_matches_no_uri(self):
         with pytest.raises(ValueError):
-            r = AATProvider({'id': 'AAT'}).find({'matches': {'type': 'close'}})
+            AATProvider({'id': 'AAT'}).find({'matches': {'type': 'close'}})
 
     def test_answer_wrong_query(self):
         with pytest.raises(ProviderUnavailableException):
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 3bd272c..67710cd 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -1,15 +1,16 @@
-# -*- coding: utf-8 -*-
 import pytest
 import rdflib
+from rdflib.namespace import SKOS
+from rdflib.plugin import PluginException
 from skosprovider.exceptions import ProviderUnavailableException
-from skosprovider_getty.utils import (
-    uri_to_graph,
-    SubClassCollector,
-    GVP,
-    ISO
-)
 
-class TestUtils(object):
+from skosprovider_getty.utils import GVP
+from skosprovider_getty.utils import ISO
+from skosprovider_getty.utils import SubClassCollector
+from skosprovider_getty.utils import uri_to_graph
+
+
+class TestUtils:
 
     def test_uri_to_graph(self):
         uri = 'http://vocab.getty.edu/aat/300007466.rdf'
@@ -18,8 +19,8 @@ def test_uri_to_graph(self):
 
     def test_uri_to_graph2(self):
         uri = 'http://vocab.getty.edu/aat/300007466'
-        with pytest.raises(TypeError):
-            res = uri_to_graph(uri)
+        with pytest.raises(PluginException):
+            uri_to_graph(uri)
 
     def test_uri_to_graph_not_found(self):
         uri = 'http://vocab.getty.edu/aat55/300zzz7466.rdf'
@@ -29,31 +30,27 @@ def test_uri_to_graph_not_found(self):
     def test_uri_to_graph_error(self):
         uri = 'http://teeezssst.teeteest.test/aat55/300zzz7466.rdf'
         with pytest.raises(ProviderUnavailableException):
-            res = uri_to_graph(uri)
+            uri_to_graph(uri)
 
     def test_get_subclasses(self):
-        from rdflib.namespace import SKOS
         subclasses = SubClassCollector(GVP)
         list_concept_subclasses = subclasses.get_subclasses(SKOS.Concept)
         assert len(list_concept_subclasses) == 8
         assert SKOS.Concept in list_concept_subclasses
 
     def test_collect_subclasses_concept(self):
-        from rdflib.namespace import SKOS
         subclasses = SubClassCollector(rdflib.Namespace("http://vocab.getty.edu/ontology#"))
         list_concept_subclasses = subclasses.collect_subclasses(SKOS.Concept)
         assert len(list_concept_subclasses) == 8
         assert SKOS.Concept in list_concept_subclasses
 
     def test_collect_subclasses_collection(self):
-        from rdflib.namespace import SKOS
         subclasses = SubClassCollector(rdflib.Namespace("http://vocab.getty.edu/ontology#"))
         list_concept_subclasses = subclasses.collect_subclasses(SKOS.Collection)
         assert len(list_concept_subclasses) == 5
         assert SKOS.Collection in list_concept_subclasses
 
     def test_collect_subclasses_(self):
-        from rdflib.namespace import SKOS
         subclasses = SubClassCollector(GVP)
         list_concept_subclasses = subclasses.collect_subclasses(ISO.ThesaurusArray)
         assert len(list_concept_subclasses) == 4