diff --git a/src/pretix/base/management/commands/check_order_transactions.py b/src/pretix/base/management/commands/check_order_transactions.py
index e7b8b57ed1..2fa5d67413 100644
--- a/src/pretix/base/management/commands/check_order_transactions.py
+++ b/src/pretix/base/management/commands/check_order_transactions.py
@@ -104,4 +104,4 @@ class Command(BaseCommand):
             print(f"Error in order {o.full_code}: status={o.status}, sum(positions)+sum(fees)={o.position_total + o.fee_total}, "
                   f"order.total={o.total}, sum(transactions)={o.tx_total}, expected={o.correct_total}, pos_cnt={o.position_cnt}, tx_pos_cnt={o.tx_cnt}")
 
-        self.stderr.write(self.style.SUCCESS(f'Check completed.'))
+        self.stderr.write(self.style.SUCCESS('Check completed.'))
diff --git a/src/pretix/base/models/checkin.py b/src/pretix/base/models/checkin.py
index bc54707b22..b49084a226 100644
--- a/src/pretix/base/models/checkin.py
+++ b/src/pretix/base/models/checkin.py
@@ -221,7 +221,7 @@ class CheckinList(LoggedModel):
             return rules
 
         if operator in ('or', 'and') and seen_nonbool:
-            raise ValidationError(f'You cannot use OR/AND logic on a level below a comparison operator.')
+            raise ValidationError('You cannot use OR/AND logic on a level below a comparison operator.')
 
         for v in values:
             cls.validate_rules(v, seen_nonbool=seen_nonbool or operator not in ('or', 'and'), depth=depth + 1)
diff --git a/src/pretix/base/services/checkin.py b/src/pretix/base/services/checkin.py
index b8f2b863ea..92fba0c7db 100644
--- a/src/pretix/base/services/checkin.py
+++ b/src/pretix/base/services/checkin.py
@@ -373,22 +373,22 @@ class SQLLogic:
                 ).astimezone(pytz.UTC))
             elif values[0] == 'date_from':
                 return Coalesce(
-                    F(f'subevent__date_from'),
-                    F(f'order__event__date_from'),
+                    F('subevent__date_from'),
+                    F('order__event__date_from'),
                 )
             elif values[0] == 'date_to':
                 return Coalesce(
-                    F(f'subevent__date_to'),
-                    F(f'subevent__date_from'),
-                    F(f'order__event__date_to'),
-                    F(f'order__event__date_from'),
+                    F('subevent__date_to'),
+                    F('subevent__date_from'),
+                    F('order__event__date_to'),
+                    F('order__event__date_from'),
                 )
             elif values[0] == 'date_admission':
                 return Coalesce(
-                    F(f'subevent__date_admission'),
-                    F(f'subevent__date_from'),
-                    F(f'order__event__date_admission'),
-                    F(f'order__event__date_from'),
+                    F('subevent__date_admission'),
+                    F('subevent__date_from'),
+                    F('order__event__date_admission'),
+                    F('order__event__date_from'),
                 )
             else:
                 raise ValueError(f'Unknown time type {values[0]}')
diff --git a/src/pretix/control/views/subevents.py b/src/pretix/control/views/subevents.py
index 349234ea76..78552bd38b 100644
--- a/src/pretix/control/views/subevents.py
+++ b/src/pretix/control/views/subevents.py
@@ -1470,7 +1470,7 @@ class SubEventBulkEdit(SubEventQueryMixin, EventPermissionRequiredMixin, FormVie
             form.is_valid() and
             self.quota_formset.is_valid() and
             (not self.list_formset or self.list_formset.is_valid()) and
-            all(f.is_valid() for f in self.itemvar_forms)and
+            all(f.is_valid() for f in self.itemvar_forms) and
             all(f.is_valid() for f in self.meta_forms)
         )
         if is_valid:
diff --git a/src/pretix/presale/ical.py b/src/pretix/presale/ical.py
index 8eeb082a6d..84d3c201f5 100644
--- a/src/pretix/presale/ical.py
+++ b/src/pretix/presale/ical.py
@@ -156,7 +156,7 @@ def get_private_icals(event, positions):
 
         vevent.add('uid').value = 'pretix-{}-{}-{}@{}'.format(
             event.organizer.slug,
-            event.organizer.slug, event.slug,
+            event.slug,
             ev.pk if not isinstance(ev, Event) else '0',
             urlparse(url).netloc
         )
diff --git a/src/setup.cfg b/src/setup.cfg
index 50e67a1cb3..f414c85e6b 100644
--- a/src/setup.cfg
+++ b/src/setup.cfg
@@ -1,5 +1,5 @@
 [flake8]
-ignore = N802,W503,E402,C901,E722,W504,E252,N812,N806,E741
+ignore = N802,W503,E402,C901,E722,W504,E252,N812,N806,N818,E741
 max-line-length = 160
 exclude = migrations,.ropeproject,static,mt940.py,_static,build,make_testdata.py,*/testutils/settings.py,tests/settings.py,pretix/base/models/__init__.py,pretix/base/secretgenerators/pretix_sig1_pb2.py,.eggs/*
 max-complexity = 11
diff --git a/src/setup.py b/src/setup.py
index 5ced27ad9d..386f161e78 100644
--- a/src/setup.py
+++ b/src/setup.py
@@ -237,13 +237,13 @@ setup(
             'coverage',
             'coveralls',
             'django-debug-toolbar==3.2.*',
-            'flake8>=3.7,<4.1',
+            'flake8==4.0.*',
             'freezegun',
-            'isort',
-            'pep8-naming',
+            'isort==5.10.*',
+            'pep8-naming==0.12.*',
             'potypo',
-            'pycodestyle==2.5.*',
-            'pyflakes>=2.1,<2.5',
+            'pycodestyle==2.8.*',
+            'pyflakes==2.4../pretix/base/models/checkin.py*',
             'pytest-cache',
             'pytest-cov',
             'pytest-django==4.*',
diff --git a/src/tests/api/test_device_event_selection.py b/src/tests/api/test_device_event_selection.py
index baa9d85ecc..9dc823d301 100644
--- a/src/tests/api/test_device_event_selection.py
+++ b/src/tests/api/test_device_event_selection.py
@@ -31,7 +31,7 @@ tz = pytz.timezone("Asia/Tokyo")
 
 @pytest.mark.django_db
 def test_no_events(device_client, device):
-    resp = device_client.get(f'/api/v1/device/eventselection?current_event=e1')
+    resp = device_client.get('/api/v1/device/eventselection?current_event=e1')
     assert resp.status_code == 404
 
 
@@ -66,26 +66,26 @@ def test_choose_between_events(device_client, device):
         resp = device_client.get(f'/api/v1/device/eventselection?current_event=e1&current_checkinlist={cl1.pk}')
         assert resp.status_code == 304
     with freeze_time("2020-01-10T16:30:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection?current_event=e1')
+        resp = device_client.get('/api/v1/device/eventselection?current_event=e1')
         assert resp.status_code == 200
-        resp = device_client.get(f'/api/v1/device/eventselection?current_event=e2')
+        resp = device_client.get('/api/v1/device/eventselection?current_event=e2')
         assert resp.status_code == 304
 
     # Next one only
     with freeze_time("2020-01-10T12:30:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.status_code == 200
         assert resp.data['event']['slug'] == 'e1'
 
     # Last one only
     with freeze_time("2020-01-10T17:30:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.status_code == 200
         assert resp.data['event']['slug'] == 'e2'
 
     # Running one
     with freeze_time("2020-01-10T14:30:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.status_code == 200
         assert resp.data['event']['slug'] == 'e1'
     with freeze_time("2020-01-10T16:01:00+09:00"):
@@ -108,11 +108,11 @@ def test_choose_between_events(device_client, device):
 
     # Switch at half-time
     with freeze_time("2020-01-10T15:29:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.status_code == 200
         assert resp.data['event']['slug'] == 'e1'
     with freeze_time("2020-01-10T15:31:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.status_code == 200
         assert resp.data['event']['slug'] == 'e2'
 
@@ -120,9 +120,9 @@ def test_choose_between_events(device_client, device):
     e2.date_admission = tz.localize(datetime(2020, 1, 10, 14, 45))
     e2.save()
     with freeze_time("2020-01-10T14:45:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection?current_event=e1')
+        resp = device_client.get('/api/v1/device/eventselection?current_event=e1')
         assert resp.status_code == 200
-        resp = device_client.get(f'/api/v1/device/eventselection?current_event=e2')
+        resp = device_client.get('/api/v1/device/eventselection?current_event=e2')
         assert resp.status_code == 304
 
 
@@ -165,21 +165,21 @@ def test_choose_between_subevents(device_client, device):
 
     # Next one only
     with freeze_time("2020-01-10T12:30:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.status_code == 200
         assert resp.data['event']['slug'] == 'e1'
         assert resp.data['subevent'] == se1.pk
 
     # Last one only
     with freeze_time("2020-01-10T17:30:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.status_code == 200
         assert resp.data['event']['slug'] == 'e1'
         assert resp.data['subevent'] == se2.pk
 
     # Running one
     with freeze_time("2020-01-10T14:30:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.status_code == 200
         assert resp.data['event']['slug'] == 'e1'
         assert resp.data['subevent'] == se1.pk
@@ -193,7 +193,7 @@ def test_choose_between_subevents(device_client, device):
 
     # Prefer the one on the same day
     with freeze_time("2020-01-10T23:59:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.status_code == 200
         assert resp.data['event']['slug'] == 'e1'
         assert resp.data['subevent'] == se2.pk
@@ -207,12 +207,12 @@ def test_choose_between_subevents(device_client, device):
 
     # Switch at half-time
     with freeze_time("2020-01-10T15:29:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.status_code == 200
         assert resp.data['event']['slug'] == 'e1'
         assert resp.data['subevent'] == se1.pk
     with freeze_time("2020-01-10T15:31:00+09:00"):
-        resp = device_client.get(f'/api/v1/device/eventselection')
+        resp = device_client.get('/api/v1/device/eventselection')
         assert resp.data['event']['slug'] == 'e1'
         assert resp.data['subevent'] == se2.pk
 
diff --git a/src/tests/api/test_exporters.py b/src/tests/api/test_exporters.py
index b6833c3ffb..17b5f8b97d 100644
--- a/src/tests/api/test_exporters.py
+++ b/src/tests/api/test_exporters.py
@@ -115,7 +115,7 @@ def test_org_list(token_client, organizer, event):
     resp = token_client.get('/api/v1/organizers/{}/exporters/'.format(organizer.slug))
     assert resp.status_code == 200
     assert c in resp.data['results']
-    resp = token_client.get('/api/v1/organizers/{}/exporters/orderlist/'.format(organizer.slug, event.slug))
+    resp = token_client.get('/api/v1/organizers/{}/exporters/orderlist/'.format(organizer.slug))
     assert resp.status_code == 200
     assert c == resp.data
 
diff --git a/src/tests/api/test_idempotency.py b/src/tests/api/test_idempotency.py
index 76d5fa3d4c..c7915523e2 100644
--- a/src/tests/api/test_idempotency.py
+++ b/src/tests/api/test_idempotency.py
@@ -133,10 +133,10 @@ def test_ignore_get(token_client, organizer, event):
 
 @pytest.mark.django_db
 def test_ignore_outside_api(token_client, organizer):
-    resp = token_client.post('/control/login'.format(organizer.slug),
+    resp = token_client.post('/control/login',
                              PAYLOAD, format='json', HTTP_X_IDEMPOTENCY_KEY='foo')
     assert resp.status_code == 200
-    resp = token_client.post('/control/invalid/'.format(organizer.slug),
+    resp = token_client.post('/control/invalid/',
                              PAYLOAD, format='json', HTTP_X_IDEMPOTENCY_KEY='foo')
     assert resp.status_code == 302
 
diff --git a/src/tests/control/test_auth.py b/src/tests/control/test_auth.py
index a6d3a4409f..0a29785f04 100644
--- a/src/tests/control/test_auth.py
+++ b/src/tests/control/test_auth.py
@@ -348,7 +348,7 @@ class Login2FAFormTest(TestCase):
         d = TOTPDevice.objects.create(user=self.user, name='test')
         totp = TOTP(d.bin_key, d.step, d.t0, d.digits, d.drift)
         totp.time = time.time()
-        response = self.client.post('/control/login/2fa'.format(d.pk), {
+        response = self.client.post('/control/login/2fa', {
             'token': str(totp.token() + 2)
         })
         self.assertEqual(response.status_code, 302)
@@ -360,7 +360,7 @@ class Login2FAFormTest(TestCase):
         d = TOTPDevice.objects.create(user=self.user, name='test')
         totp = TOTP(d.bin_key, d.step, d.t0, d.digits, d.drift)
         totp.time = time.time()
-        response = self.client.post('/control/login/2fa?next=/control/events/'.format(d.pk), {
+        response = self.client.post('/control/login/2fa?next=/control/events/', {
             'token': str(totp.token())
         })
         self.assertEqual(response.status_code, 302)
@@ -374,7 +374,7 @@ class Login2FAFormTest(TestCase):
 
         m = self.monkeypatch
         m.setattr("webauthn.WebAuthnAssertionResponse.verify", fail)
-        d = U2FDevice.objects.create(
+        U2FDevice.objects.create(
             user=self.user, name='test',
             json_data='{"appId": "https://local.pretix.eu", "keyHandle": '
                       '"j9Rkpon1J5U3eDQMM8YqAvwEapt-m87V8qdCaImiAqmvTJ'
@@ -384,7 +384,7 @@ class Login2FAFormTest(TestCase):
 
         response = self.client.get('/control/login/2fa')
         assert 'token' in response.content.decode()
-        response = self.client.post('/control/login/2fa'.format(d.pk), {
+        response = self.client.post('/control/login/2fa', {
             'token': '{"response": "true"}'
         })
         self.assertEqual(response.status_code, 302)
@@ -396,7 +396,7 @@ class Login2FAFormTest(TestCase):
         m = self.monkeypatch
         m.setattr("webauthn.WebAuthnAssertionResponse.verify", lambda *args, **kwargs: 1)
 
-        d = U2FDevice.objects.create(
+        U2FDevice.objects.create(
             user=self.user, name='test',
             json_data='{"appId": "https://local.pretix.eu", "keyHandle": '
                       '"j9Rkpon1J5U3eDQMM8YqAvwEapt-m87V8qdCaImiAqmvTJ'
@@ -406,7 +406,7 @@ class Login2FAFormTest(TestCase):
 
         response = self.client.get('/control/login/2fa')
         assert 'token' in response.content.decode()
-        response = self.client.post('/control/login/2fa'.format(d.pk), {
+        response = self.client.post('/control/login/2fa', {
             'token': '{"response": "true"}'
         })
         self.assertEqual(response.status_code, 302)
@@ -964,7 +964,7 @@ class PasswordChangeRequiredTest(TestCase):
         totp = TOTP(d.bin_key, d.step, d.t0, d.digits, d.drift)
         totp.time = time.time()
 
-        self.client.post('/control/login/2fa?next=/control/events/'.format(d.pk), {
+        self.client.post('/control/login/2fa?next=/control/events/', {
             'token': str(totp.token())
         })
         response = self.client.get('/control/events/')
diff --git a/src/tests/control/test_customer.py b/src/tests/control/test_customer.py
index 6db491eea0..e8c8097a78 100644
--- a/src/tests/control/test_customer.py
+++ b/src/tests/control/test_customer.py
@@ -145,7 +145,7 @@ def test_customer_anonymize(organizer, admin_user, customer, client, order):
 @pytest.mark.django_db
 def test_list_of_membership_types(organizer, admin_user, client, customer, membership_type):
     client.login(email='dummy@dummy.dummy', password='dummy')
-    resp = client.get('/control/organizer/dummy/membershiptypes'.format(customer.identifier))
+    resp = client.get('/control/organizer/dummy/membershiptypes')
     c = resp.content.decode()
     assert 'Week pass' in c
 
diff --git a/src/tests/control/test_giftcards.py b/src/tests/control/test_giftcards.py
index cb813da17d..855488331d 100644
--- a/src/tests/control/test_giftcards.py
+++ b/src/tests/control/test_giftcards.py
@@ -174,11 +174,11 @@ def test_card_detail_view_transact_invalid_value(organizer, admin_user, gift_car
 @pytest.mark.django_db
 def test_manage_acceptance(organizer, organizer2, admin_user, gift_card, client, team2):
     client.login(email='dummy@dummy.dummy', password='dummy')
-    client.post('/control/organizer/dummy/giftcards'.format(gift_card.pk), {
+    client.post('/control/organizer/dummy/giftcards', {
         'add': organizer2.slug
     })
     assert organizer.gift_card_issuer_acceptance.filter(issuer=organizer2).exists()
-    client.post('/control/organizer/dummy/giftcards'.format(gift_card.pk), {
+    client.post('/control/organizer/dummy/giftcards', {
         'del': organizer2.slug
     })
     assert not organizer.gift_card_issuer_acceptance.filter(issuer=organizer2).exists()
@@ -187,7 +187,7 @@ def test_manage_acceptance(organizer, organizer2, admin_user, gift_card, client,
 @pytest.mark.django_db
 def test_manage_acceptance_permission_required(organizer, organizer2, admin_user, gift_card, client):
     client.login(email='dummy@dummy.dummy', password='dummy')
-    client.post('/control/organizer/dummy/giftcards'.format(gift_card.pk), {
+    client.post('/control/organizer/dummy/giftcards', {
         'add': organizer2.slug
     })
     assert not organizer.gift_card_issuer_acceptance.filter(issuer=organizer2).exists()
diff --git a/src/tests/control/test_orders.py b/src/tests/control/test_orders.py
index 81b1c56eeb..6bcf8b9183 100644
--- a/src/tests/control/test_orders.py
+++ b/src/tests/control/test_orders.py
@@ -1978,7 +1978,7 @@ def test_refund_propose_lower_payment(client, env):
     }, follow=True)
     doc = BeautifulSoup(response.content.decode(), "lxml")
     assert doc.select("input[name=refund-{}]".format(p2.pk))[0]['value'] == '6.00'
-    assert doc.select("input[name=refund-manual]".format(p2.pk))[0]['value'] == '1.00'
+    assert doc.select("input[name=refund-manual]")[0]['value'] == '1.00'
 
 
 @pytest.mark.django_db
@@ -1999,7 +1999,7 @@ def test_refund_propose_equal_payment(client, env):
     }, follow=True)
     doc = BeautifulSoup(response.content.decode(), "lxml")
     assert doc.select("input[name=refund-{}]".format(p2.pk))[0]['value'] == '7.00'
-    assert not doc.select("input[name=refund-manual]".format(p2.pk))[0].get('value')
+    assert not doc.select("input[name=refund-manual]")[0].get('value')
 
 
 @pytest.mark.django_db
@@ -2020,7 +2020,7 @@ def test_refund_propose_higher_payment(client, env):
     }, follow=True)
     doc = BeautifulSoup(response.content.decode(), "lxml")
     assert doc.select("input[name=refund-{}]".format(p2.pk))[0]['value'] == '7.00'
-    assert not doc.select("input[name=refund-manual]".format(p2.pk))[0].get('value')
+    assert not doc.select("input[name=refund-manual]")[0].get('value')
 
 
 @pytest.mark.django_db
diff --git a/src/tests/plugins/banktransfer/test_actions.py b/src/tests/plugins/banktransfer/test_actions.py
index 7800dec479..975ce85fe2 100644
--- a/src/tests/plugins/banktransfer/test_actions.py
+++ b/src/tests/plugins/banktransfer/test_actions.py
@@ -134,7 +134,7 @@ def test_comment(env, client):
                                            amount=12, date='unknown')
     client.login(email='dummy@dummy.dummy', password='dummy')
     r = json.loads(client.post('/control/event/{}/{}/banktransfer/action/'.format(env[0].organizer.slug, env[0].slug), {
-        'action_{}'.format(trans.pk): 'comment:This is my comment'.format(env[2].code)
+        'action_{}'.format(trans.pk): 'comment:This is my comment'
     }).content.decode('utf-8'))
     assert r['status'] == 'ok'
     trans.refresh_from_db()
diff --git a/src/tests/presale/test_customer.py b/src/tests/presale/test_customer.py
index 3555e25167..05e7870926 100644
--- a/src/tests/presale/test_customer.py
+++ b/src/tests/presale/test_customer.py
@@ -151,13 +151,13 @@ def test_org_login_logout(env, client):
     })
     assert r.status_code == 302
 
-    r = client.get(f'/bigevents/account/')
+    r = client.get('/bigevents/account/')
     assert r.status_code == 200
 
     r = client.get('/bigevents/account/logout')
     assert r.status_code == 302
 
-    r = client.get(f'/bigevents/account/')
+    r = client.get('/bigevents/account/')
     assert r.status_code == 302
 
 
@@ -288,7 +288,7 @@ def test_org_order_list(env, client):
     })
     assert r.status_code == 302
 
-    r = client.get(f'/bigevents/account/')
+    r = client.get('/bigevents/account/')
     assert r.status_code == 200
     content = r.content.decode()
     assert o1.code not in content
@@ -297,7 +297,7 @@ def test_org_order_list(env, client):
 
     env[0].settings.customer_accounts_link_by_email = True
 
-    r = client.get(f'/bigevents/account/')
+    r = client.get('/bigevents/account/')
     assert r.status_code == 200
     content = r.content.decode()
     assert o1.code not in content
@@ -318,7 +318,7 @@ def test_change_name(env, client):
     })
     assert r.status_code == 302
 
-    r = client.post(f'/bigevents/account/change', {
+    r = client.post('/bigevents/account/change', {
         'name_parts_0': 'John Doe',
         'email': 'john@example.org',
     })
@@ -340,7 +340,7 @@ def test_change_email(env, client):
     })
     assert r.status_code == 302
 
-    r = client.post(f'/bigevents/account/change', {
+    r = client.post('/bigevents/account/change', {
         'name_parts_0': 'John Doe',
         'email': 'john@example.com'
     })
@@ -348,7 +348,7 @@ def test_change_email(env, client):
     customer.refresh_from_db()
     assert customer.email == 'john@example.org'
 
-    r = client.post(f'/bigevents/account/change', {
+    r = client.post('/bigevents/account/change', {
         'name_parts_0': 'John Doe',
         'email': 'john@example.com',
         'password_current': 'foo',
@@ -358,11 +358,11 @@ def test_change_email(env, client):
     assert customer.email == 'john@example.org'
     assert len(djmail.outbox) == 1
 
-    token = dumps({
+    dumps({
         'customer': customer.pk,
         'email': 'john@example.com'
     }, salt='pretix.presale.views.customer.ChangeInformationView')
-    r = client.get(f'/bigevents/account/confirmchange?token={token}')
+    r = client.get('/bigevents/account/confirmchange?token={token}')
     assert r.status_code == 302
     customer.refresh_from_db()
     assert customer.email == 'john@example.com'
@@ -381,7 +381,7 @@ def test_change_pw(env, client):
     })
     assert r.status_code == 302
 
-    r = client.post(f'/bigevents/account/password', {
+    r = client.post('/bigevents/account/password', {
         'password_current': 'invalid',
         'password': 'aYLBRNg4',
         'password_repeat': 'aYLBRNg4',
@@ -390,7 +390,7 @@ def test_change_pw(env, client):
     customer.refresh_from_db()
     assert customer.check_password('foo')
 
-    r = client.post(f'/bigevents/account/password', {
+    r = client.post('/bigevents/account/password', {
         'password_current': 'foo',
         'password': 'aYLBRNg4',
         'password_repeat': 'aYLBRNg4',