diff --git a/lib/vsc/ldap/__init__.py b/lib/vsc/ldap/__init__.py
index e711d20..7454760 100644
--- a/lib/vsc/ldap/__init__.py
+++ b/lib/vsc/ldap/__init__.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # Copyright 2009-2023 Ghent University
 #
@@ -54,7 +53,7 @@ class NoSuchUserError(Exception):
     """If a user cannot be found in the LDAP."""
     def __init__(self, name):
         """Initialisation."""
-        super(NoSuchUserError, self).__init__()
+        super().__init__()
         self.name = name
 
 
@@ -62,7 +61,7 @@ class UserAlreadyExistsError(Exception):
     """If a user already is present in the LDAP, i.e., the dn already exists."""
     def __init__(self, name):
         """Initialisation."""
-        super(UserAlreadyExistsError, self).__init__()
+        super().__init__()
         self.name = name
 
 
@@ -70,7 +69,7 @@ class NoSuchVoError(Exception):
     """If a VO cannot be found in the LDAP."""
     def __init__(self, name):
         """Initialisation."""
-        super(NoSuchVoError, self).__init__()
+        super().__init__()
         self.name = name
 
 
@@ -78,7 +77,7 @@ class NoSuchGroupError(Exception):
     """If a group cannot be found in the LDAP."""
     def __init__(self, name):
         """Initialisation."""
-        super(NoSuchGroupError, self).__init__()
+        super().__init__()
         self.name = name
 
 
@@ -86,7 +85,7 @@ class NoSuchProjectError(Exception):
     """If a project cannot be found in the LDAP."""
     def __init__(self, name):
         """Initialisation."""
-        super(NoSuchProjectError, self).__init__()
+        super().__init__()
         self.name = name
 
 
@@ -94,5 +93,5 @@ class GroupAlreadyExistsError(Exception):
     """If a group is already present, i.e., the dn already exists."""
     def __init__(self, name):
         """Initialisation."""
-        super(GroupAlreadyExistsError, self).__init__()
+        super().__init__()
         self.name = name
diff --git a/lib/vsc/ldap/filters.py b/lib/vsc/ldap/filters.py
index 5993db6..3803245 100644
--- a/lib/vsc/ldap/filters.py
+++ b/lib/vsc/ldap/filters.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # Copyright 2009-2023 Ghent University
 #
@@ -83,7 +82,7 @@ class LdapFilterError(Exception):
     pass
 
 
-class LdapFilter(object):
+class LdapFilter:
     """Representing an LDAP filter with operators between the filter values.
 
     This is implemented as a tree, where the nodes are the operations, e.g.,
@@ -172,7 +171,7 @@ def _to_string(self, previous_operator=None):
 
         if self.left is None:
             # single value, self.root should be a string not representing an operator
-            return "(%s)" % (self.root)
+            return f"({self.root})"
 
         left_string = self.left._to_string(self.root)
         if not self.right is None:
@@ -181,9 +180,9 @@ def _to_string(self, previous_operator=None):
             right_string = ""
 
         if self.root == previous_operator:
-            return "%s%s" % (left_string, right_string)
+            return f"{left_string}{right_string}"
         else:
-            return "(%s%s%s)" % (self.root, left_string, right_string)
+            return f"({self.root}{left_string}{right_string})"
 
     def _combine(self, operator, value=None):
         """Updates the tree with a new root, i.e., the given operator and
@@ -215,7 +214,7 @@ def __init__(self, value, timestamp, comparator):
                          will be converted to a format LDAP groks.
         @type comparator: string representing a comparison operation, e.g., <=, >=
         """
-        super(TimestampFilter, self).__init__(value)
+        super().__init__(value)
         self.timestamp = convert_timestamp(timestamp)[1]
         if comparator != '>=' and comparator != '<=':
             raise LdapFilterError()
@@ -223,9 +222,7 @@ def __init__(self, value, timestamp, comparator):
 
     def __str__(self):
         """Converts the filter to an LDAP understood string."""
-        return "(& (modifyTimestamp%s%s) %s)" % (self.comparator,
-                                                 self.timestamp,
-                                                 super(TimestampFilter, self).__str__())
+        return f"(& (modifyTimestamp{self.comparator}{self.timestamp}) {super().__str__()})"
 
 
 class NewerThanFilter(TimestampFilter):
@@ -237,7 +234,7 @@ def __init__(self, value, timestamp):
         @type timestamp: string or datetime instance representing a timestamp. This value
                          will be converted to a format LDAP groks.
         """
-        super(NewerThanFilter, self).__init__(value, timestamp, '>=')
+        super().__init__(value, timestamp, '>=')
 
 
 class OlderThanFilter(TimestampFilter):
@@ -249,32 +246,32 @@ def __init__(self, value, timestamp):
         @type timestamp: string or datetime instance representing a timestamp. This value
                          will be converted to a format LDAP groks.
         """
-        super(OlderThanFilter, self).__init__(value, timestamp, '<=')
+        super().__init__(value, timestamp, '<=')
 
 
 class CnFilter(LdapFilter):
     """Representa a filter that matches a given common name."""
 
     def __init__(self, cn):
-        super(CnFilter, self).__init__("cn=%s" % (cn))
+        super().__init__(f"cn={cn}")
 
 
 class MemberFilter(LdapFilter):
     """Represents a filter that looks if a member is listed in the memberUid."""
 
     def __init__(self, user_id):
-        super(MemberFilter, self).__init__("memberUid=%s" % (user_id))
+        super().__init__(f"memberUid={user_id}")
 
 
 class LoginFilter(LdapFilter):
     """Represents a filter that looks up a user based on his institute login name."""
 
     def __init__(self, login):
-        super(LoginFilter, self).__init__("login=%s" % (login))
+        super().__init__(f"login={login}")
 
 
 class InstituteFilter(LdapFilter):
     """Represents a filter that looks up a user based on his institute login name."""
 
     def __init__(self, institute):
-        super(InstituteFilter, self).__init__("institute=%s" % (institute))
+        super().__init__(f"institute={institute}")
diff --git a/lib/vsc/ldap/group.py b/lib/vsc/ldap/group.py
index 598bcc0..df28056 100644
--- a/lib/vsc/ldap/group.py
+++ b/lib/vsc/ldap/group.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # Copyright 2009-2023 Ghent University
 #
@@ -69,12 +68,12 @@ def __init__(self, group_id):
 
         @raise NoSuchGroupError if the group cannot be found.
         """
-        super(LdapGroup, self).__init__(self.LDAP_OBJECT_CLASS_ATTRIBUTES)
+        super().__init__(self.LDAP_OBJECT_CLASS_ATTRIBUTES)
         self.group_id = group_id
 
     def get_ldap_info(self):
         """Retrieve the data from the LDAP to initially fill up the ldap_info field."""
-        group_ldap_info = self.ldap_query.group_filter_search("cn=%s" % (self.group_id))
+        group_ldap_info = self.ldap_query.group_filter_search(f"cn={self.group_id}")
         if len(group_ldap_info) == 0:
             logging.error("Could not find a group in the LDAP with the ID %s, raising NoSuchGroupError",
                 self.group_id)
diff --git a/lib/vsc/ldap/project.py b/lib/vsc/ldap/project.py
index 3dbdcde..4e2b9b8 100644
--- a/lib/vsc/ldap/project.py
+++ b/lib/vsc/ldap/project.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # Copyright 2009-2023 Ghent University
 #
@@ -74,12 +73,12 @@ def __init__(self, project_id):
 
         @raise NoSuchProjectError if the project cannot be found.
         """
-        super(LdapProject, self).__init__(self.LDAP_OBJECT_CLASS_ATTRIBUTES)
+        super().__init__(self.LDAP_OBJECT_CLASS_ATTRIBUTES)
         self.project_id = project_id
 
     def get_ldap_info(self):
         """Retrieve the data from the LDAP to initially fill up the ldap_info field."""
-        project_ldap_info = self.ldap_query.project_filter_search("cn=%s" % (self.project_id))
+        project_ldap_info = self.ldap_query.project_filter_search(f"cn={self.project_id}")
         if len(project_ldap_info) == 0:
             logging.error("Could not find a project in the LDAP with the ID %s, raising NoSuchGroupError",
                            self.project_id)
@@ -113,7 +112,7 @@ def get_for_member(user):
         """
 
         # get all the projects in the LDAP
-        projects_info = user.ldap_query.projects_filter_search("memberUid=%s" % user.user_id)
+        projects_info = user.ldap_query.projects_filter_search(f"memberUid={user.user_id}")
 
         projects = []
         for p_info in projects_info:
diff --git a/lib/vsc/ldap/user.py b/lib/vsc/ldap/user.py
index f11c811..171a5b1 100644
--- a/lib/vsc/ldap/user.py
+++ b/lib/vsc/ldap/user.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # Copyright 2009-2023 Ghent University
 #
@@ -78,7 +77,7 @@ def __init__(self, user_id):
 
         @type user_id: string representing the ID of the user, i.e., his cn in LDAP.
         """
-        super(LdapUser, self).__init__(self.LDAP_OBJECT_CLASS_ATTRIBUTES)
+        super().__init__(self.LDAP_OBJECT_CLASS_ATTRIBUTES)
 
         self.user_id = user_id
         self.vo = None
diff --git a/lib/vsc/ldap/utils.py b/lib/vsc/ldap/utils.py
index f691a8a..a837ec7 100644
--- a/lib/vsc/ldap/utils.py
+++ b/lib/vsc/ldap/utils.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # Copyright 2009-2023 Ghent University
 #
@@ -45,7 +44,7 @@
 EMPTY_GECOS_DURING_MODIFY = "EMPTYGECOSDURINGMODIFY"
 
 
-class LdapConfiguration(object):
+class LdapConfiguration:
     """Represents some LDAP configuration.
 
     @param url: url to ldap server (default None)
@@ -78,7 +77,7 @@ class SchemaConfiguration(LdapConfiguration):
     """Represents an LDAP configuration with some extra schema-related information."""
 
     def __init__(self):
-        super(SchemaConfiguration, self).__init__()
+        super().__init__()
 
         self.user_dn_base = None
         self.group_dn_base = None
@@ -91,7 +90,7 @@ def __init__(self):
         self.vo_multi_value_attributes = None
 
 
-class LdapConnection(object):
+class LdapConnection:
     """Represents a connection to an LDAP server.
 
     - Offers a set of convenience functions for querying and updating the server.
@@ -111,6 +110,7 @@ def __init__(self, configuration):
         """
         self.configuration = configuration
         self.ldap_connection = None
+        self.ldap_url = None
 
     @TryOrFail(3, (ldap.LDAPError,), 10)
     def connect(self):
@@ -193,7 +193,7 @@ def search_sync(self, ldap_filter, base, attributes=None):
             self.bind()
 
         # ldap_filter can also be an LdapFilter instance
-        ldap_filter = "%s" % ldap_filter
+        ldap_filter = f"{ldap_filter}"
 
         try:
             res = self.ldap_connection.search_s(base, ldap.SCOPE_SUBTREE, ldap_filter, attributes)
@@ -218,7 +218,7 @@ def search_async_timeout(self, ldap_filter, base, attributes=None, timeout=10):
         attrs_only = False
 
         # filter can also be LdapFilter instance
-        ldap_filter = "%s" % ldap_filter
+        ldap_filter = f"{ldap_filter}"
 
         try:
             res = self.ldap_connection.search_st(base, ldap.SCOPE_SUBTREE, ldap_filter, attributes, attrs_only, timeout)
@@ -274,8 +274,8 @@ def add(self, dn, attributes):
         if self.ldap_connection is None:
             self.bind()
 
-        changes = [(k, [v]) for (k, v) in attributes if not type(v) == list]
-        changes.extend([(k, v) for (k, v) in attributes if type(v) == list])
+        changes = [(k, [v]) for (k, v) in attributes if not isinstance(v, list)]
+        changes.extend([(k, v) for (k, v) in attributes if isinstance(v, list)])
         logging.info("Adding for dn=%s with changes = %s", dn, changes)
 
         try:
@@ -462,8 +462,8 @@ def user_search(self, user_id, institute, attributes=None):
 
         @returns: a dictionary, with the values for the requested attributes for the given user
         """
-        login_filter = LdapFilter("instituteLogin=%s" % (user_id))
-        institute_filter = LdapFilter("institute=%s" % (institute))
+        login_filter = LdapFilter(f"instituteLogin={user_id}")
+        institute_filter = LdapFilter(f"institute={institute}")
 
         result = self.user_filter_search(login_filter & institute_filter, attributes)
         logging.debug("user_search for %s, %s yields %s", user_id, institute, result)
@@ -504,7 +504,7 @@ def __modify(self, current, dn, attributes):
         current_ = {}
         for key in attributes.keys():
             current_[key] = current.get(key, [])
-            if current_[key] is '':
+            if current_[key] == '':
                 logging.warning("Replacing empty string for key %s with %s before making modlist for dn %s",
                     key, EMPTY_GECOS_DURING_MODIFY, dn)
                 current_[key] = EMPTY_GECOS_DURING_MODIFY  # hack to allow replacing empty strings
@@ -525,7 +525,7 @@ def group_modify(self, cn, attributes):
 
         @raise: NoSuchGroupError
         """
-        dn = "cn=%s,%s" % (cn, self.configuration.group_dn_base)
+        dn = f"cn={cn},{self.configuration.group_dn_base}"
         current = self.group_filter_search(CnFilter(cn))
         if current is None:
             logging.error("group_modify did not find group with cn = %s (dn = %s)", cn, dn)
@@ -542,7 +542,7 @@ def user_modify(self, cn, attributes):
 
         @raise: NoSuchUserError
         """
-        dn = "cn=%s,%s" % (cn, self.configuration.user_dn_base)
+        dn = f"cn={cn},{self.configuration.user_dn_base}"
         current = self.user_filter_search(CnFilter(cn))
         if current is None:
             logging.error("user_modify did not find user with cn = %s (dn = %s)", cn, dn)
@@ -559,7 +559,7 @@ def project_modify(self, cn, attributes):
 
         @raise: NoSuchProjectError
         """
-        dn = "cn=%s,%s" % (cn, self.configuration.project_dn_base)
+        dn = f"cn={cn},{self.configuration.project_dn_base}"
         current = self.project_filter_search(CnFilter(cn))
         if current is None:
             logging.error("project_modify did not find project with cn = %s (dn = %s)", cn, dn)
@@ -574,8 +574,8 @@ def user_add(self, cn, attributes):
         @type cn: string representing the common name for the user. Together with the subtree, this forms the dn.
         @type attributes: dictionary with attributes for which a value should be added
         """
-        dn = "cn=%s,%s" % (cn, self.configuration.user_dn_base)
-        attributes = {key:[v.encode("utf-8") if type(v) == str else v for v in values]
+        dn = f"cn={cn},{self.configuration.user_dn_base}"
+        attributes = {key:[v.encode("utf-8") if isinstance(v, str) else v for v in values]
                       for key, values in attributes.items()}
         self.ldap.add(dn, attributes.items())
 
@@ -585,8 +585,8 @@ def group_add(self, cn, attributes):
         @type cn: string representing the common name for the group. Together with the subtree, this forms the dn.
         @type attributes: dictionary with attributes for which a value should be added
         """
-        dn = "cn=%s,%s" % (cn, self.configuration.group_dn_base)
-        attributes = {key:[v.encode("utf-8") if type(v) == str else v for v in values]
+        dn = f"cn={cn},{self.configuration.group_dn_base}"
+        attributes = {key:[v.encode("utf-8") if isinstance(v, str) else v for v in values]
                       for key, values in attributes.items()}
         self.ldap.add(dn, attributes.items())
 
@@ -596,8 +596,8 @@ def project_add(self, cn, attributes):
         @type cn: string representing the common name for the project. Together with the subtree, this forms the dn.
         @type attributes: dictionary with attributes for which a value should be added
         """
-        dn = "cn=%s,%s" % (cn, self.configuration.project_dn_base)
-        attributes = {key:[v.encode("utf-8") if type(v) == str else v for v in values]
+        dn = f"cn={cn},{self.configuration.project_dn_base}"
+        attributes = {key:[v.encode("utf-8") if isinstance(v, str) else v for v in values]
                       for key, values in attributes.items()}
         self.ldap.add(dn, attributes.items())
 
@@ -678,7 +678,7 @@ def get_schema(self, ldap_obj_class_name_or_oid, reload=False, do_reload=False):
         return self.schema[ldap_obj_class_name_or_oid]
 
 
-class LdapEntity(object):
+class LdapEntity:
     """Base class for all things LDAP that work on a higher level."""
 
     def __init__(self, object_classes=None):
@@ -703,7 +703,6 @@ def modify_ldap(self, attributes):
 
         Should be iplemented by deriving classes.
         """
-        pass
 
     def __getattr__(self, name):
         """Getter for the LdapUser fields. Only accessed for fields that are in
@@ -758,7 +757,6 @@ def __setattr__(self, name, value):
                 except ldap.LDAPError:
                     logging.error("Could not save the new value %s for %s with cn=%s to the LDAP",
                                    value, name, self.vsc_user_id)
-                    pass
             else:
                 object.__setattr__(self, name, value)
         except AttributeError:
diff --git a/lib/vsc/ldap/vo.py b/lib/vsc/ldap/vo.py
index fb50bba..2b9fc95 100644
--- a/lib/vsc/ldap/vo.py
+++ b/lib/vsc/ldap/vo.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # Copyright 2009-2023 Ghent University
 #
@@ -69,7 +68,7 @@ def __init__(self, vo_id):
 
         @raise NoSuchVoError if the VO cannot be found.
         """
-        super(LdapVo, self).__init__(vo_id)
+        super().__init__(vo_id)
 
     def get_ldap_info(self):
         """Retrieve the data from the LDAP to initially fill up the ldap_info field."""
@@ -98,9 +97,9 @@ def get_for_member(user):
 
         # there should be at most a single VO.
         if len(vos) > 1:
-            msg = "Found multiple VOs for the given user (%s), vos = %s" % (user, vos)
+            msg = f"Found multiple VOs for the given user ({user}), vos = {vos}"
             logging.error(msg)
-            raise Exception(msg)
+            raise ValueError(msg)
 
         vo_info = vos[0]
 
diff --git a/setup.py b/setup.py
index afa0754..eca1722 100644
--- a/setup.py
+++ b/setup.py
@@ -1,5 +1,4 @@
 #!/usr/bin/env python
-# -*- coding: utf-8 -*-
 ##
 # Copyright 2009-2012 Ghent University
 #
@@ -43,7 +42,7 @@
         'future >= 0.16.0',
         'python-ldap',
     ],
-    'version': '2.2.2',
+    'version': '2.2.3',
     'author': [ag, kh, sdw, wdp, jt],
     'maintainer': [ag],
 }
diff --git a/test/filters.py b/test/filters.py
index 3fba227..3118fd9 100644
--- a/test/filters.py
+++ b/test/filters.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # Copyright 2009-2023 Ghent University
 #
@@ -38,7 +37,7 @@
 from vsc.ldap.filters import LdapFilter
 
 
-class SingleChoiceGenerator(object):
+class SingleChoiceGenerator:
     """Provides a list of exhausting choices, reducing the choices until in each iteration."""
     def __init__(self, values):
         self.values = values
@@ -52,7 +51,7 @@ def next(self):
         return v
 
 
-class LdapFilterGenerator(object):
+class LdapFilterGenerator:
     """Generates random LdapFilter instances"""
 
     def __init__(self):
@@ -79,12 +78,12 @@ def next(self):
         attribute_choice = SingleChoiceGenerator(attributes)
 
         size = random.randint(1, random.randint(1, len(self.attributes)))
-        for d in range(0, size):
+        for _ in range(0, size):
 
             op = random.choice(self.operators)
             at = attribute_choice.next()
 
-            new = LdapFilter("%s=%s" % (at, ''.join([random.choice(string.printable) for x in range(16)])))
+            new = LdapFilter(f"{at}={''.join([random.choice(string.printable) for x in range(16)])}")
 
             if not ldap_filter:
                 ldap_filter = LdapFilter(new)
@@ -107,11 +106,11 @@ def test_and(self):
         """Test the and operator for combining two filters."""
         left = LFG.next()
         right = LFG.next()
-        combination = (left & right)
+        combination = left & right
 
-        left_string = "%s" % (left)
-        right_string = "%s" % (right)
-        combination_string = "%s" % (combination)
+        left_string = f"{left}"
+        right_string = f"{right}"
+        combination_string = f"{combination}"
 
         self.assertTrue(len(combination_string) <= 3 + len(left_string) + len(right_string))
         self.assertTrue(combination_string[0] == '(')
@@ -127,9 +126,9 @@ def test_or(self):
         right = LFG.next()
         combination = left | right
 
-        left_string = "%s" % (left)
-        right_string = "%s" % (right)
-        combination_string = "%s" % (combination)
+        left_string = f"{left}"
+        right_string = f"{right}"
+        combination_string = f"{combination}"
 
         self.assertTrue(len(combination_string) <= 3 + len(left_string) + len(right_string))
         self.assertTrue(combination_string[0] == '(')
@@ -144,7 +143,7 @@ def test_negate(self):
         left = LFG.next()
         negation = left.negate()
 
-        negation_string = "%s" % (negation)
+        negation_string = f"{negation}"
 
         self.assertTrue(negation_string[0] == '(')
         self.assertTrue(negation_string[1] == '!')
@@ -155,9 +154,9 @@ def test_from_list_and(self):
         fs = [LFG.next() for x in range(random.randint(2,30))]
 
         combination = LdapFilter.from_list(lambda x, y: x & y, fs)
-        combination_string = "%s" % (combination)
+        combination_string = f"{combination}"
 
-        self.assertTrue(len(combination_string) <= 3 + sum(map(lambda f: len("%s" % (f)), fs)))
+        self.assertTrue(len(combination_string) <= 3 + sum(map(lambda f: len(f"{f}"), fs)))
 
         self.assertTrue(combination_string[0] == '(')
         self.assertTrue(combination_string[1] == '&')
diff --git a/tox.ini b/tox.ini
index 159ce91..1fcd1e0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -3,7 +3,7 @@
 # DO NOT EDIT MANUALLY
 
 [tox]
-envlist = py36
+envlist = py36,py39
 skipsdist = true
 
 [testenv]
diff --git a/vsc-ci.ini b/vsc-ci.ini
new file mode 100644
index 0000000..ebb0e46
--- /dev/null
+++ b/vsc-ci.ini
@@ -0,0 +1,2 @@
+[vsc-ci]
+py39_tests_must_pass=1