diff --git a/data/hooks/diagnosis/00-basesystem.py b/data/hooks/diagnosis/00-basesystem.py
index d003c2670..a60070b5a 100644
--- a/data/hooks/diagnosis/00-basesystem.py
+++ b/data/hooks/diagnosis/00-basesystem.py
@@ -42,10 +42,8 @@ class BaseSystemDiagnoser(Diagnoser):
         elif os.path.exists("/sys/devices/virtual/dmi/id/sys_vendor"):
             model = read_file("/sys/devices/virtual/dmi/id/sys_vendor").strip()
             if os.path.exists("/sys/devices/virtual/dmi/id/product_name"):
-                model = "%s %s" % (
-                    model,
-                    read_file("/sys/devices/virtual/dmi/id/product_name").strip(),
-                )
+                product_name = read_file("/sys/devices/virtual/dmi/id/product_name").strip()
+                model = f"{model} {product_name}"
             hardware["data"]["model"] = model
             hardware["details"] = ["diagnosis_basesystem_hardware_model"]
 
@@ -116,7 +114,7 @@ class BaseSystemDiagnoser(Diagnoser):
         bad_sury_packages = list(self.bad_sury_packages())
         if bad_sury_packages:
             cmd_to_fix = "apt install --allow-downgrades " + " ".join(
-                ["%s=%s" % (package, version) for package, version in bad_sury_packages]
+                [f"{package}={version}" for package, version in bad_sury_packages]
             )
             yield dict(
                 meta={"test": "packages_from_sury"},
diff --git a/data/hooks/diagnosis/10-ip.py b/data/hooks/diagnosis/10-ip.py
index 408019668..1c6c5a4b3 100644
--- a/data/hooks/diagnosis/10-ip.py
+++ b/data/hooks/diagnosis/10-ip.py
@@ -167,10 +167,7 @@ class IPDiagnoser(Diagnoser):
 
         assert (
             resolvers != []
-        ), "Uhoh, need at least one IPv%s DNS resolver in %s ..." % (
-            protocol,
-            resolver_file,
-        )
+        ), f"Uhoh, need at least one IPv{protocol} DNS resolver in {resolver_file} ..."
 
         # So let's try to ping the first 4~5 resolvers (shuffled)
         # If we succesfully ping any of them, we conclude that we are indeed connected
@@ -220,9 +217,9 @@ class IPDiagnoser(Diagnoser):
         try:
             return download_text(url, timeout=30).strip()
         except Exception as e:
-            self.logger_debug(
-                "Could not get public IPv%s : %s" % (str(protocol), str(e))
-            )
+            protocol = str(protocol)
+            e = str(e)
+            self.logger_debug(f"Could not get public IPv{protocol} : {e}")
             return None
 
 
diff --git a/data/hooks/diagnosis/50-systemresources.py b/data/hooks/diagnosis/50-systemresources.py
index a662e392e..bdea0ea16 100644
--- a/data/hooks/diagnosis/50-systemresources.py
+++ b/data/hooks/diagnosis/50-systemresources.py
@@ -132,7 +132,7 @@ class SystemResourcesDiagnoser(Diagnoser):
             d for d in disk_partitions if d.mountpoint in ["/", "/var"]
         ]
         main_space = sum(
-            [psutil.disk_usage(d.mountpoint).total for d in main_disk_partitions]
+            psutil.disk_usage(d.mountpoint).total for d in main_disk_partitions
         )
         if main_space < 10 * GB:
             yield dict(
@@ -156,7 +156,7 @@ class SystemResourcesDiagnoser(Diagnoser):
         kills_count = self.recent_kills_by_oom_reaper()
         if kills_count:
             kills_summary = "\n".join(
-                ["%s (x%s)" % (proc, count) for proc, count in kills_count]
+                [f"{proc} (x{count})" for proc, count in kills_count]
             )
 
             yield dict(
@@ -202,9 +202,11 @@ def human_size(bytes_):
     # Adapted from https://stackoverflow.com/a/1094933
     for unit in ["", "ki", "Mi", "Gi", "Ti", "Pi", "Ei", "Zi"]:
         if abs(bytes_) < 1024.0:
-            return "%s %sB" % (round_(bytes_), unit)
+            bytes_ = round_(bytes_)
+            return f"{bytes_} {unit}B"
         bytes_ /= 1024.0
-    return "%s %sB" % (round_(bytes_), "Yi")
+    bytes_ = round_(bytes_)
+    return f"{bytes_} YiB"
 
 
 def round_(n):
diff --git a/doc/generate_helper_doc.py b/doc/generate_helper_doc.py
index f2d5bf444..689904a8a 100644
--- a/doc/generate_helper_doc.py
+++ b/doc/generate_helper_doc.py
@@ -107,7 +107,7 @@ class Parser:
                 else:
                     # We're getting out of a comment bloc, we should find
                     # the name of the function
-                    assert len(line.split()) >= 1, "Malformed line %s in %s" % (
+                    assert len(line.split()) >= 1, "Malformed line {} in {}".format(
                         i,
                         self.filename,
                     )
diff --git a/src/yunohost/app.py b/src/yunohost/app.py
index ece44f172..d5e57d6cf 100644
--- a/src/yunohost/app.py
+++ b/src/yunohost/app.py
@@ -122,7 +122,7 @@ def app_list(full=False, installed=False, filter=None):
         try:
             app_info_dict = app_info(app_id, full=full)
         except Exception as e:
-            logger.error("Failed to read info for %s : %s" % (app_id, e))
+            logger.error(f"Failed to read info for {app_id} : {e}")
             continue
         app_info_dict["id"] = app_id
         out.append(app_info_dict)
@@ -1219,7 +1219,8 @@ def app_setting(app, key, value=None, delete=False):
         )
 
         permissions = user_permission_list(full=True, apps=[app])["permissions"]
-        permission_name = "%s.legacy_%s_uris" % (app, key.split("_")[0])
+        key_ = key.split("_")[0]
+        permission_name = f"{app}.legacy_{key_}_uris"
         permission = permissions.get(permission_name)
 
         # GET
@@ -1562,11 +1563,7 @@ def app_action_run(operation_logger, app, action, args=None):
         shutil.rmtree(tmp_workdir_for_app)
 
     if retcode not in action_declaration.get("accepted_return_codes", [0]):
-        msg = "Error while executing action '%s' of app '%s': return code %s" % (
-            action,
-            app,
-            retcode,
-        )
+        msg = f"Error while executing action '{action}' of app '{app}': return code {retcode}"
         operation_logger.error(msg)
         raise YunohostError(msg, raw_msg=True)
 
@@ -1989,7 +1986,8 @@ def _set_default_ask_questions(arguments):
                 for question in questions_with_default
             ):
                 # The key is for example "app_manifest_install_ask_domain"
-                key = "app_manifest_%s_ask_%s" % (script_name, arg["name"])
+                arg_name = arg["name"]
+                key = f"app_manifest_{script_name}_ask_{arg_name}"
                 arg["ask"] = m18n.n(key)
 
             # Also it in fact doesn't make sense for any of those questions to have an example value nor a default value...
@@ -2397,7 +2395,8 @@ def _make_environment_for_app_script(
         env_dict["YNH_APP_BASEDIR"] = workdir
 
     for arg_name, arg_value in args.items():
-        env_dict["YNH_%s%s" % (args_prefix, arg_name.upper())] = str(arg_value)
+        arg_name_upper = arg_name.upper()
+        env_dict[f"YNH_{args_prefix}{arg_name_upper}"] = str(arg_value)
 
     return env_dict
 
diff --git a/src/yunohost/app_catalog.py b/src/yunohost/app_catalog.py
index e4ffa1db6..0f0e1ae46 100644
--- a/src/yunohost/app_catalog.py
+++ b/src/yunohost/app_catalog.py
@@ -217,7 +217,7 @@ def _load_apps_catalog():
             )
         except Exception as e:
             raise YunohostError(
-                "Unable to read cache for apps_catalog %s : %s" % (cache_file, e),
+                f"Unable to read cache for apps_catalog {cache_file} : {e}",
                 raw_msg=True,
             )
 
diff --git a/src/yunohost/backup.py b/src/yunohost/backup.py
index f68e59b13..ebfb23ab0 100644
--- a/src/yunohost/backup.py
+++ b/src/yunohost/backup.py
@@ -80,7 +80,7 @@ MB_ALLOWED_TO_ORGANIZE = 10
 logger = getActionLogger("yunohost.backup")
 
 
-class BackupRestoreTargetsManager(object):
+class BackupRestoreTargetsManager:
 
     """
     BackupRestoreTargetsManager manage the targets
@@ -1570,7 +1570,7 @@ class RestoreManager:
 #
 # Backup methods                                                            #
 #
-class BackupMethod(object):
+class BackupMethod:
 
     """
     BackupMethod is an abstract class that represents a way to backup and
@@ -2380,7 +2380,7 @@ def backup_list(with_info=False, human_readable=False):
     # Get local archives sorted according to last modification time
     # (we do a realpath() to resolve symlinks)
     archives = glob("%s/*.tar.gz" % ARCHIVES_PATH) + glob("%s/*.tar" % ARCHIVES_PATH)
-    archives = set([os.path.realpath(archive) for archive in archives])
+    archives = {os.path.realpath(archive) for archive in archives}
     archives = sorted(archives, key=lambda x: os.path.getctime(x))
     # Extract only filename without the extension
 
@@ -2420,7 +2420,7 @@ def backup_download(name):
         )
         return
 
-    archive_file = "%s/%s.tar" % (ARCHIVES_PATH, name)
+    archive_file = f"{ARCHIVES_PATH}/{name}.tar"
 
     # Check file exist (even if it's a broken symlink)
     if not os.path.lexists(archive_file):
@@ -2462,7 +2462,7 @@ def backup_info(name, with_details=False, human_readable=False):
     elif name.endswith(".tar"):
         name = name[: -len(".tar")]
 
-    archive_file = "%s/%s.tar" % (ARCHIVES_PATH, name)
+    archive_file = f"{ARCHIVES_PATH}/{name}.tar"
 
     # Check file exist (even if it's a broken symlink)
     if not os.path.lexists(archive_file):
@@ -2480,7 +2480,7 @@ def backup_info(name, with_details=False, human_readable=False):
                 "backup_archive_broken_link", path=archive_file
             )
 
-    info_file = "%s/%s.info.json" % (ARCHIVES_PATH, name)
+    info_file = f"{ARCHIVES_PATH}/{name}.info.json"
 
     if not os.path.exists(info_file):
         tar = tarfile.open(
@@ -2591,10 +2591,10 @@ def backup_delete(name):
 
     hook_callback("pre_backup_delete", args=[name])
 
-    archive_file = "%s/%s.tar" % (ARCHIVES_PATH, name)
+    archive_file = f"{ARCHIVES_PATH}/{name}.tar"
     if not os.path.exists(archive_file) and os.path.exists(archive_file + ".gz"):
         archive_file += ".gz"
-    info_file = "%s/%s.info.json" % (ARCHIVES_PATH, name)
+    info_file = f"{ARCHIVES_PATH}/{name}.info.json"
 
     files_to_delete = [archive_file, info_file]
 
@@ -2693,5 +2693,5 @@ def binary_to_human(n, customary=False):
     for s in reversed(symbols):
         if n >= prefix[s]:
             value = float(n) / prefix[s]
-            return "%.1f%s" % (value, s)
+            return "{:.1f}{}".format(value, s)
     return "%s" % n
diff --git a/src/yunohost/certificate.py b/src/yunohost/certificate.py
index 2679b2429..79e3ae092 100644
--- a/src/yunohost/certificate.py
+++ b/src/yunohost/certificate.py
@@ -143,11 +143,7 @@ def _certificate_install_selfsigned(domain_list, force=False):
 
         # Paths of files and folder we'll need
         date_tag = datetime.utcnow().strftime("%Y%m%d.%H%M%S")
-        new_cert_folder = "%s/%s-history/%s-selfsigned" % (
-            CERT_FOLDER,
-            domain,
-            date_tag,
-        )
+        new_cert_folder = f"{CERT_FOLDER}/{domain}-history/{date_tag}-selfsigned"
 
         conf_template = os.path.join(SSL_DIR, "openssl.cnf")
 
@@ -300,10 +296,7 @@ def _certificate_install_letsencrypt(
         try:
             _fetch_and_enable_new_certificate(domain, staging, no_checks=no_checks)
         except Exception as e:
-            msg = "Certificate installation for %s failed !\nException: %s" % (
-                domain,
-                e,
-            )
+            msg = f"Certificate installation for {domain} failed !\nException: {e}"
             logger.error(msg)
             operation_logger.error(msg)
             if no_checks:
@@ -456,39 +449,25 @@ def _email_renewing_failed(domain, exception_message, stack=""):
     subject_ = "Certificate renewing attempt for %s failed!" % domain
 
     logs = _tail(50, "/var/log/yunohost/yunohost-cli.log")
-    text = """
-An attempt for renewing the certificate for domain %s failed with the following
+    message = f"""\
+From: {from_}
+To: {to_}
+Subject: {subject_}
+
+
+An attempt for renewing the certificate for domain {domain} failed with the following
 error :
 
-%s
-%s
+{exception_message}
+{stack}
 
 Here's the tail of /var/log/yunohost/yunohost-cli.log, which might help to
 investigate :
 
-%s
+{logs}
 
 -- Certificate Manager
-
-""" % (
-        domain,
-        exception_message,
-        stack,
-        logs,
-    )
-
-    message = """\
-From: %s
-To: %s
-Subject: %s
-
-%s
-""" % (
-        from_,
-        to_,
-        subject_,
-        text,
-    )
+"""
 
     import smtplib
 
@@ -532,7 +511,7 @@ def _fetch_and_enable_new_certificate(domain, staging=False, no_checks=False):
     # Prepare certificate signing request
     logger.debug("Prepare key and certificate signing request (CSR) for %s...", domain)
 
-    domain_key_file = "%s/%s.pem" % (TMP_FOLDER, domain)
+    domain_key_file = f"{TMP_FOLDER}/{domain}.pem"
     _generate_key(domain_key_file)
     _set_permissions(domain_key_file, "root", "ssl-cert", 0o640)
 
@@ -541,7 +520,7 @@ def _fetch_and_enable_new_certificate(domain, staging=False, no_checks=False):
     # Sign the certificate
     logger.debug("Now using ACME Tiny to sign the certificate...")
 
-    domain_csr_file = "%s/%s.csr" % (TMP_FOLDER, domain)
+    domain_csr_file = f"{TMP_FOLDER}/{domain}.csr"
 
     if staging:
         certification_authority = STAGING_CERTIFICATION_AUTHORITY
@@ -580,12 +559,7 @@ def _fetch_and_enable_new_certificate(domain, staging=False, no_checks=False):
     else:
         folder_flag = "letsencrypt"
 
-    new_cert_folder = "%s/%s-history/%s-%s" % (
-        CERT_FOLDER,
-        domain,
-        date_tag,
-        folder_flag,
-    )
+    new_cert_folder = f"{CERT_FOLDER}/{domain}-history/{date_tag}-{folder_flag}"
 
     os.makedirs(new_cert_folder)
 
@@ -642,7 +616,7 @@ def _prepare_certificate_signing_request(domain, key_file, output_folder):
             csr.add_extensions(
                 [
                     crypto.X509Extension(
-                        "subjectAltName".encode("utf8"),
+                        b"subjectAltName",
                         False,
                         ("DNS:" + subdomain).encode("utf8"),
                     )
@@ -844,7 +818,7 @@ def _backup_current_cert(domain):
     cert_folder_domain = os.path.join(CERT_FOLDER, domain)
 
     date_tag = datetime.utcnow().strftime("%Y%m%d.%H%M%S")
-    backup_folder = "%s-backups/%s" % (cert_folder_domain, date_tag)
+    backup_folder = f"{cert_folder_domain}-backups/{date_tag}"
 
     shutil.copytree(cert_folder_domain, backup_folder)
 
diff --git a/src/yunohost/data_migrations/0015_migrate_to_buster.py b/src/yunohost/data_migrations/0015_migrate_to_buster.py
index 4f2d4caf8..626dd682a 100644
--- a/src/yunohost/data_migrations/0015_migrate_to_buster.py
+++ b/src/yunohost/data_migrations/0015_migrate_to_buster.py
@@ -269,14 +269,14 @@ class MyMigration(Migration):
                 % default_crt
             )
 
-            os.system("mv %s %s.old" % (default_crt, default_crt))
-            os.system("mv %s %s.old" % (default_key, default_key))
+            os.system("mv {} {}.old".format(default_crt, default_crt))
+            os.system("mv {} {}.old".format(default_key, default_key))
             ret = os.system("/usr/share/yunohost/hooks/conf_regen/02-ssl init")
 
             if ret != 0 or not os.path.exists(default_crt):
                 logger.error("Upgrading the certificate failed ... reverting")
-                os.system("mv %s.old %s" % (default_crt, default_crt))
-                os.system("mv %s.old %s" % (default_key, default_key))
+                os.system("mv {}.old {}".format(default_crt, default_crt))
+                os.system("mv {}.old {}".format(default_key, default_key))
 
         signatures = {cert: check_output(cmd % cert) for cert in active_certs}
 
diff --git a/src/yunohost/diagnosis.py b/src/yunohost/diagnosis.py
index 4ac5e2731..dfe58685e 100644
--- a/src/yunohost/diagnosis.py
+++ b/src/yunohost/diagnosis.py
@@ -640,7 +640,7 @@ class Diagnoser:
         elif ipversion == 6:
             socket.getaddrinfo = getaddrinfo_ipv6_only
 
-        url = "https://%s/%s" % (DIAGNOSIS_SERVER, uri)
+        url = "https://{}/{}".format(DIAGNOSIS_SERVER, uri)
         try:
             r = requests.post(url, json=data, timeout=timeout)
         finally:
@@ -679,7 +679,7 @@ def _email_diagnosis_issues():
     from yunohost.domain import _get_maindomain
 
     maindomain = _get_maindomain()
-    from_ = "diagnosis@%s (Automatic diagnosis on %s)" % (maindomain, maindomain)
+    from_ = "diagnosis@{} (Automatic diagnosis on {})".format(maindomain, maindomain)
     to_ = "root"
     subject_ = "Issues found by automatic diagnosis on %s" % maindomain
 
@@ -692,16 +692,16 @@ def _email_diagnosis_issues():
     content = _dump_human_readable_reports(issues)
 
     message = """\
-From: %s
-To: %s
-Subject: %s
+From: {}
+To: {}
+Subject: {}
 
-%s
+{}
 
 ---
 
-%s
-""" % (
+{}
+""".format(
         from_,
         to_,
         subject_,
diff --git a/src/yunohost/dns.py b/src/yunohost/dns.py
index 534ade918..23c641a35 100644
--- a/src/yunohost/dns.py
+++ b/src/yunohost/dns.py
@@ -762,7 +762,7 @@ def domain_dns_push(operation_logger, domain, dry_run=False, force=False, purge=
     changes = {"delete": [], "update": [], "create": [], "unchanged": []}
 
     type_and_names = sorted(
-        set([(r["type"], r["name"]) for r in current_records + wanted_records])
+        {(r["type"], r["name"]) for r in current_records + wanted_records}
     )
     comparison = {
         type_and_name: {"current": [], "wanted": []} for type_and_name in type_and_names
diff --git a/src/yunohost/dyndns.py b/src/yunohost/dyndns.py
index 4f4dc1d1f..8748c1c00 100644
--- a/src/yunohost/dyndns.py
+++ b/src/yunohost/dyndns.py
@@ -151,7 +151,7 @@ def dyndns_subscribe(operation_logger, domain=None, key=None):
         try:
             error = json.loads(r.text)["error"]
         except Exception:
-            error = 'Server error, code: %s. (Message: "%s")' % (r.status_code, r.text)
+            error = f'Server error, code: {r.status_code}. (Message: "{r.text}")'
         raise YunohostError("dyndns_registration_failed", error=error)
 
     # Yunohost regen conf will add the dyndns cron job if a private key exists
@@ -196,7 +196,7 @@ def dyndns_update(
 
     # If key is not given, pick the first file we find with the domain given
     elif key is None:
-        keys = glob.glob("/etc/yunohost/dyndns/K{0}.+*.private".format(domain))
+        keys = glob.glob(f"/etc/yunohost/dyndns/K{domain}.+*.private")
 
         if not keys:
             raise YunohostValidationError("dyndns_key_not_found")
@@ -263,14 +263,14 @@ def dyndns_update(
             return None
 
         raise YunohostError(
-            "Failed to resolve %s for %s" % (rdtype, domain), raw_msg=True
+            f"Failed to resolve {rdtype} for {domain}", raw_msg=True
         )
 
     old_ipv4 = resolve_domain(domain, "A")
     old_ipv6 = resolve_domain(domain, "AAAA")
 
-    logger.debug("Old IPv4/v6 are (%s, %s)" % (old_ipv4, old_ipv6))
-    logger.debug("Requested IPv4/v6 are (%s, %s)" % (ipv4, ipv6))
+    logger.debug(f"Old IPv4/v6 are ({old_ipv4}, {old_ipv6})")
+    logger.debug(f"Requested IPv4/v6 are ({ipv4}, {ipv6})")
 
     # no need to update
     if (not force and not dry_run) and (old_ipv4 == ipv4 and old_ipv6 == ipv6):
diff --git a/src/yunohost/hook.py b/src/yunohost/hook.py
index 98b624f12..7b03b2e9b 100644
--- a/src/yunohost/hook.py
+++ b/src/yunohost/hook.py
@@ -156,7 +156,7 @@ def hook_list(action, list_by="name", show_info=False):
                 try:
                     d[priority].add(name)
                 except KeyError:
-                    d[priority] = set([name])
+                    d[priority] = {name}
 
     elif list_by == "name" or list_by == "folder":
         if show_info:
@@ -197,7 +197,7 @@ def hook_list(action, list_by="name", show_info=False):
                 or (f.startswith("__") and f.endswith("__"))
             ):
                 continue
-            path = "%s%s/%s" % (folder, action, f)
+            path = f"{folder}{action}/{f}"
             priority, name = _extract_filename_parts(f)
             _append_hook(d, priority, name, path)
 
@@ -407,7 +407,7 @@ def _hook_exec_bash(path, args, chdir, env, user, return_format, loggers):
     if not chdir:
         # use the script directory as current one
         chdir, cmd_script = os.path.split(path)
-        cmd_script = "./{0}".format(cmd_script)
+        cmd_script = f"./{cmd_script}"
     else:
         cmd_script = path
 
diff --git a/src/yunohost/log.py b/src/yunohost/log.py
index 0e534f9f8..d28a35e18 100644
--- a/src/yunohost/log.py
+++ b/src/yunohost/log.py
@@ -469,7 +469,7 @@ class RedactingFormatter(Formatter):
             )
 
 
-class OperationLogger(object):
+class OperationLogger:
 
     """
     Instances of this class represents unit operation done on the ynh instance.
@@ -544,7 +544,7 @@ class OperationLogger(object):
             # We use proc.open_files() to list files opened / actively used by this proc
             # We only keep files matching a recent yunohost operation log
             active_logs = sorted(
-                [f.path for f in proc.open_files() if f.path in recent_operation_logs],
+                (f.path for f in proc.open_files() if f.path in recent_operation_logs),
                 key=os.path.getctime,
                 reverse=True,
             )
diff --git a/src/yunohost/permission.py b/src/yunohost/permission.py
index 1856046d6..9a46cad27 100644
--- a/src/yunohost/permission.py
+++ b/src/yunohost/permission.py
@@ -139,7 +139,8 @@ def user_permission_list(
                 continue
             main_perm_label = permissions[main_perm_name]["label"]
             infos["sublabel"] = infos["label"]
-            infos["label"] = "%s (%s)" % (main_perm_label, infos["label"])
+            label_ = infos["label"]
+            infos["label"] = f"{main_perm_label} ({label_})"
 
     if short:
         permissions = list(permissions.keys())
@@ -664,13 +665,11 @@ def permission_sync_to_user():
         currently_allowed_users = set(permission_infos["corresponding_users"])
 
         # These are the users that should be allowed because they are member of a group that is allowed for this permission ...
-        should_be_allowed_users = set(
-            [
+        should_be_allowed_users = {
                 user
                 for group in permission_infos["allowed"]
                 for user in groups[group]["members"]
-            ]
-        )
+        }
 
         # Note that a LDAP operation with the same value that is in LDAP crash SLAP.
         # So we need to check before each ldap operation that we really change something in LDAP
diff --git a/src/yunohost/regenconf.py b/src/yunohost/regenconf.py
index 1beef8a44..adec5508d 100644
--- a/src/yunohost/regenconf.py
+++ b/src/yunohost/regenconf.py
@@ -638,12 +638,9 @@ def _process_regen_conf(system_conf, new_conf=None, save=True):
 
     """
     if save:
-        backup_path = os.path.join(
-            BACKUP_CONF_DIR,
-            "{0}-{1}".format(
-                system_conf.lstrip("/"), datetime.utcnow().strftime("%Y%m%d.%H%M%S")
-            ),
-        )
+        system_conf_ = system_conf.lstrip("/")
+        now_ = datetime.utcnow().strftime("%Y%m%d.%H%M%S")
+        backup_path = os.path.join(BACKUP_CONF_DIR, f"{system_conf_}-{now_}")
         backup_dir = os.path.dirname(backup_path)
 
         if not os.path.isdir(backup_dir):
diff --git a/src/yunohost/service.py b/src/yunohost/service.py
index f200d08c0..4f453dfe9 100644
--- a/src/yunohost/service.py
+++ b/src/yunohost/service.py
@@ -625,7 +625,7 @@ def _run_service_command(action, service):
             % (action, ", ".join(possible_actions))
         )
 
-    cmd = "systemctl %s %s" % (action, service)
+    cmd = f"systemctl {action} {service}"
 
     need_lock = services[service].get("need_lock", False) and action in [
         "start",
@@ -673,7 +673,7 @@ def _give_lock(action, service, p):
     else:
         systemctl_PID_name = "ControlPID"
 
-    cmd_get_son_PID = "systemctl show %s -p %s" % (service, systemctl_PID_name)
+    cmd_get_son_PID = f"systemctl show {service} -p {systemctl_PID_name}"
     son_PID = 0
     # As long as we did not found the PID and that the command is still running
     while son_PID == 0 and p.poll() is None:
@@ -686,9 +686,7 @@ def _give_lock(action, service, p):
     # If we found a PID
     if son_PID != 0:
         # Append the PID to the lock file
-        logger.debug(
-            "Giving a lock to PID %s for service %s !" % (str(son_PID), service)
-        )
+        logger.debug(f"Giving a lock to PID {son_PID} for service {service} !")
         append_to_file(MOULINETTE_LOCK, "\n%s" % str(son_PID))
 
     return son_PID
@@ -865,9 +863,7 @@ def _get_journalctl_logs(service, number="all"):
     systemd_service = services.get(service, {}).get("actual_systemd_service", service)
     try:
         return check_output(
-            "journalctl --no-hostname --no-pager -u {0} -n{1}".format(
-                systemd_service, number
-            )
+            f"journalctl --no-hostname --no-pager -u {systemd_service} -n{number}"
         )
     except Exception:
         import traceback
diff --git a/src/yunohost/settings.py b/src/yunohost/settings.py
index d59b41a58..eddb30764 100644
--- a/src/yunohost/settings.py
+++ b/src/yunohost/settings.py
@@ -224,7 +224,7 @@ def settings_set(key, value):
     try:
         trigger_post_change_hook(key, old_value, value)
     except Exception as e:
-        logger.error("Post-change hook for setting %s failed : %s" % (key, e))
+        logger.error(f"Post-change hook for setting {key} failed : {e}")
         raise
 
 
diff --git a/src/yunohost/tests/test_app_catalog.py b/src/yunohost/tests/test_app_catalog.py
index 8423b868e..e9ecb1c12 100644
--- a/src/yunohost/tests/test_app_catalog.py
+++ b/src/yunohost/tests/test_app_catalog.py
@@ -132,7 +132,7 @@ def test_apps_catalog_update_nominal(mocker):
     catalog = app_catalog(with_categories=True)
 
     assert "apps" in catalog
-    assert set(catalog["apps"].keys()) == set(["foo", "bar"])
+    assert set(catalog["apps"].keys()) == {"foo", "bar"}
 
     assert "categories" in catalog
     assert [c["id"] for c in catalog["categories"]] == ["yolo", "swag"]
diff --git a/src/yunohost/tests/test_app_config.py b/src/yunohost/tests/test_app_config.py
index 0eb813672..8de03bfd5 100644
--- a/src/yunohost/tests/test_app_config.py
+++ b/src/yunohost/tests/test_app_config.py
@@ -70,7 +70,7 @@ def legacy_app(request):
 
     app_install(
         os.path.join(get_test_apps_dir(), "legacy_app_ynh"),
-        args="domain=%s&path=%s&is_public=%s" % (main_domain, "/", 1),
+        args="domain={}&path={}&is_public={}".format(main_domain, "/", 1),
         force=True,
     )
 
diff --git a/src/yunohost/tests/test_apps.py b/src/yunohost/tests/test_apps.py
index 22e18ec9a..2a808b5bd 100644
--- a/src/yunohost/tests/test_apps.py
+++ b/src/yunohost/tests/test_apps.py
@@ -111,7 +111,7 @@ def secondary_domain(request):
 
 def app_expected_files(domain, app):
 
-    yield "/etc/nginx/conf.d/%s.d/%s.conf" % (domain, app)
+    yield "/etc/nginx/conf.d/{}.d/{}.conf".format(domain, app)
     if app.startswith("legacy_app"):
         yield "/var/www/%s/index.html" % app
     yield "/etc/yunohost/apps/%s/settings.yml" % app
@@ -152,7 +152,7 @@ def install_legacy_app(domain, path, public=True):
 
     app_install(
         os.path.join(get_test_apps_dir(), "legacy_app_ynh"),
-        args="domain=%s&path=%s&is_public=%s" % (domain, path, 1 if public else 0),
+        args="domain={}&path={}&is_public={}".format(domain, path, 1 if public else 0),
         force=True,
     )
 
@@ -170,7 +170,7 @@ def install_break_yo_system(domain, breakwhat):
 
     app_install(
         os.path.join(get_test_apps_dir(), "break_yo_system_ynh"),
-        args="domain=%s&breakwhat=%s" % (domain, breakwhat),
+        args="domain={}&breakwhat={}".format(domain, breakwhat),
         force=True,
     )
 
@@ -338,7 +338,7 @@ def test_legacy_app_failed_remove(mocker, secondary_domain):
 
     # The remove script runs with set -eu and attempt to remove this
     # file without -f, so will fail if it's not there ;)
-    os.remove("/etc/nginx/conf.d/%s.d/%s.conf" % (secondary_domain, "legacy_app"))
+    os.remove("/etc/nginx/conf.d/{}.d/{}.conf".format(secondary_domain, "legacy_app"))
 
     # TODO / FIXME : can't easily validate that 'app_not_properly_removed'
     # is triggered for weird reasons ...
diff --git a/src/yunohost/tests/test_appurl.py b/src/yunohost/tests/test_appurl.py
index 00bfe5c58..c036ae28a 100644
--- a/src/yunohost/tests/test_appurl.py
+++ b/src/yunohost/tests/test_appurl.py
@@ -99,7 +99,7 @@ def test_registerurl():
 
     app_install(
         os.path.join(get_test_apps_dir(), "register_url_app_ynh"),
-        args="domain=%s&path=%s" % (maindomain, "/urlregisterapp"),
+        args="domain={}&path={}".format(maindomain, "/urlregisterapp"),
         force=True,
     )
 
@@ -109,7 +109,7 @@ def test_registerurl():
     with pytest.raises(YunohostError):
         app_install(
             os.path.join(get_test_apps_dir(), "register_url_app_ynh"),
-            args="domain=%s&path=%s" % (maindomain, "/urlregisterapp"),
+            args="domain={}&path={}".format(maindomain, "/urlregisterapp"),
             force=True,
         )
 
@@ -119,7 +119,7 @@ def test_registerurl_baddomain():
     with pytest.raises(YunohostError):
         app_install(
             os.path.join(get_test_apps_dir(), "register_url_app_ynh"),
-            args="domain=%s&path=%s" % ("yolo.swag", "/urlregisterapp"),
+            args="domain={}&path={}".format("yolo.swag", "/urlregisterapp"),
             force=True,
         )
 
@@ -234,7 +234,7 @@ def test_normalize_permission_path_with_unknown_domain():
 def test_normalize_permission_path_conflicting_path():
     app_install(
         os.path.join(get_test_apps_dir(), "register_url_app_ynh"),
-        args="domain=%s&path=%s" % (maindomain, "/url/registerapp"),
+        args="domain={}&path={}".format(maindomain, "/url/registerapp"),
         force=True,
     )
 
diff --git a/src/yunohost/tests/test_backuprestore.py b/src/yunohost/tests/test_backuprestore.py
index 6e2c3b514..bfed5082a 100644
--- a/src/yunohost/tests/test_backuprestore.py
+++ b/src/yunohost/tests/test_backuprestore.py
@@ -139,7 +139,7 @@ def app_is_installed(app):
 
     # These are files we know should be installed by the app
     app_files = []
-    app_files.append("/etc/nginx/conf.d/%s.d/%s.conf" % (maindomain, app))
+    app_files.append("/etc/nginx/conf.d/{}.d/{}.conf".format(maindomain, app))
     app_files.append("/var/www/%s/index.html" % app)
     app_files.append("/etc/importantfile")
 
@@ -214,7 +214,7 @@ def install_app(app, path, additionnal_args=""):
 
     app_install(
         os.path.join(get_test_apps_dir(), app),
-        args="domain=%s&path=%s%s" % (maindomain, path, additionnal_args),
+        args="domain={}&path={}{}".format(maindomain, path, additionnal_args),
         force=True,
     )
 
diff --git a/src/yunohost/tests/test_changeurl.py b/src/yunohost/tests/test_changeurl.py
index e375bd9f0..04cb4a1a9 100644
--- a/src/yunohost/tests/test_changeurl.py
+++ b/src/yunohost/tests/test_changeurl.py
@@ -26,7 +26,7 @@ def teardown_function(function):
 def install_changeurl_app(path):
     app_install(
         os.path.join(get_test_apps_dir(), "change_url_app_ynh"),
-        args="domain=%s&path=%s" % (maindomain, path),
+        args="domain={}&path={}".format(maindomain, path),
         force=True,
     )
 
diff --git a/src/yunohost/tests/test_permission.py b/src/yunohost/tests/test_permission.py
index 00799d0fd..01b62f2a8 100644
--- a/src/yunohost/tests/test_permission.py
+++ b/src/yunohost/tests/test_permission.py
@@ -347,7 +347,7 @@ def check_permission_for_apps():
     # {"bar", "foo"}
     # and compare this to the list of installed apps ...
 
-    app_perms_prefix = set(p.split(".")[0] for p in app_perms)
+    app_perms_prefix = {p.split(".")[0] for p in app_perms}
 
     assert set(_installed_apps()) == app_perms_prefix
 
@@ -398,7 +398,7 @@ def test_permission_list():
     assert res["wiki.main"]["allowed"] == ["all_users"]
     assert res["blog.main"]["allowed"] == ["alice"]
     assert res["blog.api"]["allowed"] == ["visitors"]
-    assert set(res["wiki.main"]["corresponding_users"]) == set(["alice", "bob"])
+    assert set(res["wiki.main"]["corresponding_users"]) == {"alice", "bob"}
     assert res["blog.main"]["corresponding_users"] == ["alice"]
     assert res["blog.api"]["corresponding_users"] == []
     assert res["wiki.main"]["url"] == "/"
@@ -442,7 +442,7 @@ def test_permission_create_main(mocker):
     res = user_permission_list(full=True)["permissions"]
     assert "site.main" in res
     assert res["site.main"]["allowed"] == ["all_users"]
-    assert set(res["site.main"]["corresponding_users"]) == set(["alice", "bob"])
+    assert set(res["site.main"]["corresponding_users"]) == {"alice", "bob"}
     assert res["site.main"]["protected"] is False
 
 
@@ -630,8 +630,8 @@ def test_permission_add_group(mocker):
         user_permission_update("wiki.main", add="alice")
 
     res = user_permission_list(full=True)["permissions"]
-    assert set(res["wiki.main"]["allowed"]) == set(["all_users", "alice"])
-    assert set(res["wiki.main"]["corresponding_users"]) == set(["alice", "bob"])
+    assert set(res["wiki.main"]["allowed"]) == {"all_users", "alice"}
+    assert set(res["wiki.main"]["corresponding_users"]) == {"alice", "bob"}
 
 
 def test_permission_remove_group(mocker):
@@ -680,7 +680,7 @@ def test_permission_reset(mocker):
 
     res = user_permission_list(full=True)["permissions"]
     assert res["blog.main"]["allowed"] == ["all_users"]
-    assert set(res["blog.main"]["corresponding_users"]) == set(["alice", "bob"])
+    assert set(res["blog.main"]["corresponding_users"]) == {"alice", "bob"}
 
 
 def test_permission_reset_idempotency():
@@ -690,7 +690,7 @@ def test_permission_reset_idempotency():
 
     res = user_permission_list(full=True)["permissions"]
     assert res["blog.main"]["allowed"] == ["all_users"]
-    assert set(res["blog.main"]["corresponding_users"]) == set(["alice", "bob"])
+    assert set(res["blog.main"]["corresponding_users"]) == {"alice", "bob"}
 
 
 def test_permission_change_label(mocker):
@@ -1013,9 +1013,9 @@ def test_permission_app_install():
     assert res["permissions_app.dev"]["url"] == "/dev"
 
     assert res["permissions_app.main"]["allowed"] == ["all_users"]
-    assert set(res["permissions_app.main"]["corresponding_users"]) == set(
-        ["alice", "bob"]
-    )
+    assert set(res["permissions_app.main"]["corresponding_users"]) == {
+        "alice", "bob"
+    }
 
     assert res["permissions_app.admin"]["allowed"] == ["alice"]
     assert res["permissions_app.admin"]["corresponding_users"] == ["alice"]
diff --git a/src/yunohost/tests/test_questions.py b/src/yunohost/tests/test_questions.py
index c21ff8c40..5917d32d4 100644
--- a/src/yunohost/tests/test_questions.py
+++ b/src/yunohost/tests/test_questions.py
@@ -1977,7 +1977,7 @@ def test_question_file_from_api():
 
     from base64 import b64encode
 
-    b64content = b64encode("helloworld".encode())
+    b64content = b64encode(b"helloworld")
     questions = [
         {
             "name": "some_file",
diff --git a/src/yunohost/tests/test_user-group.py b/src/yunohost/tests/test_user-group.py
index d65366a9a..e561118e0 100644
--- a/src/yunohost/tests/test_user-group.py
+++ b/src/yunohost/tests/test_user-group.py
@@ -281,7 +281,7 @@ def test_update_group_add_user(mocker):
         user_group_update("dev", add=["bob"])
 
     group_res = user_group_list()["groups"]
-    assert set(group_res["dev"]["members"]) == set(["alice", "bob"])
+    assert set(group_res["dev"]["members"]) == {"alice", "bob"}
 
 
 def test_update_group_add_user_already_in(mocker):
diff --git a/src/yunohost/tools.py b/src/yunohost/tools.py
index fb9839814..679b4d16e 100644
--- a/src/yunohost/tools.py
+++ b/src/yunohost/tools.py
@@ -224,7 +224,7 @@ def tools_postinstall(
     disk_partitions = sorted(psutil.disk_partitions(), key=lambda k: k.mountpoint)
     main_disk_partitions = [d for d in disk_partitions if d.mountpoint in ["/", "/var"]]
     main_space = sum(
-        [psutil.disk_usage(d.mountpoint).total for d in main_disk_partitions]
+        psutil.disk_usage(d.mountpoint).total for d in main_disk_partitions
     )
     GB = 1024 ** 3
     if not force_diskspace and main_space < 10 * GB:
@@ -1107,7 +1107,7 @@ def _tools_migrations_run_before_app_restore(backup_version, app_id):
                 raise
 
 
-class Migration(object):
+class Migration:
 
     # Those are to be implemented by daughter classes
 
diff --git a/src/yunohost/user.py b/src/yunohost/user.py
index c9f70e152..78fda8d09 100644
--- a/src/yunohost/user.py
+++ b/src/yunohost/user.py
@@ -97,7 +97,7 @@ def user_list(fields=None):
         and values[0].strip() == "/bin/false",
     }
 
-    attrs = set(["uid"])
+    attrs = {"uid"}
     users = {}
 
     if not fields:
@@ -166,7 +166,7 @@ def user_create(
             # On affiche les differents domaines possibles
             Moulinette.display(m18n.n("domains_available"))
             for domain in domain_list()["domains"]:
-                Moulinette.display("- {}".format(domain))
+                Moulinette.display(f"- {domain}")
 
             maindomain = _get_maindomain()
             domain = Moulinette.prompt(
@@ -215,7 +215,7 @@ def user_create(
         uid_guid_found = uid not in all_uid and uid not in all_gid
 
     # Adapt values for LDAP
-    fullname = "%s %s" % (firstname, lastname)
+    fullname = f"{firstname} {lastname}"
 
     attr_dict = {
         "objectClass": [
@@ -333,8 +333,8 @@ def user_delete(operation_logger, username, purge=False, from_import=False):
     subprocess.call(["nscd", "-i", "passwd"])
 
     if purge:
-        subprocess.call(["rm", "-rf", "/home/{0}".format(username)])
-        subprocess.call(["rm", "-rf", "/var/mail/{0}".format(username)])
+        subprocess.call(["rm", "-rf", f"/home/{username}"])
+        subprocess.call(["rm", "-rf", f"/var/mail/{username}"])
 
     hook_callback("post_user_delete", args=[username, purge])
 
@@ -1334,9 +1334,9 @@ def user_ssh_remove_key(username, key):
 def _convertSize(num, suffix=""):
     for unit in ["K", "M", "G", "T", "P", "E", "Z"]:
         if abs(num) < 1024.0:
-            return "%3.1f%s%s" % (num, unit, suffix)
+            return "{:3.1f}{}{}".format(num, unit, suffix)
         num /= 1024.0
-    return "%.1f%s%s" % (num, "Yi", suffix)
+    return "{:.1f}{}{}".format(num, "Yi", suffix)
 
 
 def _hash_user_password(password):
diff --git a/src/yunohost/utils/config.py b/src/yunohost/utils/config.py
index 5d1d1f9d2..e3b09f870 100644
--- a/src/yunohost/utils/config.py
+++ b/src/yunohost/utils/config.py
@@ -678,7 +678,7 @@ class ConfigPanel:
                         yield (panel, section, option)
 
 
-class Question(object):
+class Question:
     hide_user_input_in_prompt = False
     pattern: Optional[Dict] = None
 
diff --git a/src/yunohost/utils/network.py b/src/yunohost/utils/network.py
index 4474af14f..28dcb204c 100644
--- a/src/yunohost/utils/network.py
+++ b/src/yunohost/utils/network.py
@@ -44,7 +44,7 @@ def get_public_ip(protocol=4):
     ):
         ip = read_file(cache_file).strip()
         ip = ip if ip else None  # Empty file (empty string) means there's no IP
-        logger.debug("Reusing IPv%s from cache: %s" % (protocol, ip))
+        logger.debug(f"Reusing IPv{protocol} from cache: {ip}")
     else:
         ip = get_public_ip_from_remote_server(protocol)
         logger.debug("IP fetched: %s" % ip)
@@ -87,7 +87,7 @@ def get_public_ip_from_remote_server(protocol=4):
     try:
         return download_text(url, timeout=30).strip()
     except Exception as e:
-        logger.debug("Could not get public IPv%s : %s" % (str(protocol), str(e)))
+        logger.debug(f"Could not get public IPv{protocol} : {e}")
         return None
 
 
diff --git a/src/yunohost/utils/password.py b/src/yunohost/utils/password.py
index 188850183..9fff5ece7 100644
--- a/src/yunohost/utils/password.py
+++ b/src/yunohost/utils/password.py
@@ -51,7 +51,7 @@ def assert_password_is_strong_enough(profile, password):
     PasswordValidator(profile).validate(password)
 
 
-class PasswordValidator(object):
+class PasswordValidator:
     def __init__(self, profile):
         """
         Initialize a password validator.
diff --git a/src/yunohost/utils/yunopaste.py b/src/yunohost/utils/yunopaste.py
index 0c3e3c998..35e829991 100644
--- a/src/yunohost/utils/yunopaste.py
+++ b/src/yunohost/utils/yunopaste.py
@@ -49,7 +49,7 @@ def yunopaste(data):
             raw_msg=True,
         )
 
-    return "%s/raw/%s" % (paste_server, url)
+    return "{}/raw/{}".format(paste_server, url)
 
 
 def anonymize(data):
diff --git a/src/yunohost/vendor/acme_tiny/acme_tiny.py b/src/yunohost/vendor/acme_tiny/acme_tiny.py
index 3c13d13ec..0d2534df9 100644
--- a/src/yunohost/vendor/acme_tiny/acme_tiny.py
+++ b/src/yunohost/vendor/acme_tiny/acme_tiny.py
@@ -38,7 +38,7 @@ def get_crt(
         )
         out, err = proc.communicate(cmd_input)
         if proc.returncode != 0:
-            raise IOError("{0}\n{1}".format(err_msg, err))
+            raise IOError("{}\n{}".format(err_msg, err))
         return out
 
     # helper function - make request and automatically parse json response
@@ -74,7 +74,7 @@ def get_crt(
             raise IndexError(resp_data)  # allow 100 retrys for bad nonces
         if code not in [200, 201, 204]:
             raise ValueError(
-                "{0}:\nUrl: {1}\nData: {2}\nResponse Code: {3}\nResponse: {4}".format(
+                "{}:\nUrl: {}\nData: {}\nResponse Code: {}\nResponse: {}".format(
                     err_msg, url, data, code, resp_data
                 )
             )
@@ -89,7 +89,7 @@ def get_crt(
             {"jwk": jwk} if acct_headers is None else {"kid": acct_headers["Location"]}
         )
         protected64 = _b64(json.dumps(protected).encode("utf8"))
-        protected_input = "{0}.{1}".format(protected64, payload64).encode("utf8")
+        protected_input = "{}.{}".format(protected64, payload64).encode("utf8")
         out = _cmd(
             ["openssl", "dgst", "-sha256", "-sign", account_key],
             stdin=subprocess.PIPE,
@@ -125,8 +125,8 @@ def get_crt(
     pub_hex, pub_exp = re.search(
         pub_pattern, out.decode("utf8"), re.MULTILINE | re.DOTALL
     ).groups()
-    pub_exp = "{0:x}".format(int(pub_exp))
-    pub_exp = "0{0}".format(pub_exp) if len(pub_exp) % 2 else pub_exp
+    pub_exp = "{:x}".format(int(pub_exp))
+    pub_exp = "0{}".format(pub_exp) if len(pub_exp) % 2 else pub_exp
     alg = "RS256"
     jwk = {
         "e": _b64(binascii.unhexlify(pub_exp.encode("utf-8"))),
@@ -140,9 +140,9 @@ def get_crt(
     log.info("Parsing CSR...")
     out = _cmd(
         ["openssl", "req", "-in", csr, "-noout", "-text"],
-        err_msg="Error loading {0}".format(csr),
+        err_msg="Error loading {}".format(csr),
     )
-    domains = set([])
+    domains = set()
     common_name = re.search(r"Subject:.*? CN\s?=\s?([^\s,;/]+)", out.decode("utf8"))
     if common_name is not None:
         domains.add(common_name.group(1))
@@ -155,7 +155,7 @@ def get_crt(
         for san in subject_alt_names.group(1).split(", "):
             if san.startswith("DNS:"):
                 domains.add(san[4:])
-    log.info("Found domains: {0}".format(", ".join(domains)))
+    log.info("Found domains: {}".format(", ".join(domains)))
 
     # get the ACME directory of urls
     log.info("Getting directory...")
@@ -178,7 +178,7 @@ def get_crt(
             {"contact": contact},
             "Error updating contact details",
         )
-        log.info("Updated contact details:\n{0}".format("\n".join(account["contact"])))
+        log.info("Updated contact details:\n{}".format("\n".join(account["contact"])))
 
     # create a new order
     log.info("Creating new order...")
@@ -194,46 +194,46 @@ def get_crt(
             auth_url, None, "Error getting challenges"
         )
         domain = authorization["identifier"]["value"]
-        log.info("Verifying {0}...".format(domain))
+        log.info("Verifying {}...".format(domain))
 
         # find the http-01 challenge and write the challenge file
         challenge = [c for c in authorization["challenges"] if c["type"] == "http-01"][
             0
         ]
         token = re.sub(r"[^A-Za-z0-9_\-]", "_", challenge["token"])
-        keyauthorization = "{0}.{1}".format(token, thumbprint)
+        keyauthorization = "{}.{}".format(token, thumbprint)
         wellknown_path = os.path.join(acme_dir, token)
         with open(wellknown_path, "w") as wellknown_file:
             wellknown_file.write(keyauthorization)
 
         # check that the file is in place
         try:
-            wellknown_url = "http://{0}/.well-known/acme-challenge/{1}".format(
+            wellknown_url = "http://{}/.well-known/acme-challenge/{}".format(
                 domain, token
             )
             assert disable_check or _do_request(wellknown_url)[0] == keyauthorization
         except (AssertionError, ValueError) as e:
             raise ValueError(
-                "Wrote file to {0}, but couldn't download {1}: {2}".format(
+                "Wrote file to {}, but couldn't download {}: {}".format(
                     wellknown_path, wellknown_url, e
                 )
             )
 
         # say the challenge is done
         _send_signed_request(
-            challenge["url"], {}, "Error submitting challenges: {0}".format(domain)
+            challenge["url"], {}, "Error submitting challenges: {}".format(domain)
         )
         authorization = _poll_until_not(
             auth_url,
             ["pending"],
-            "Error checking challenge status for {0}".format(domain),
+            "Error checking challenge status for {}".format(domain),
         )
         if authorization["status"] != "valid":
             raise ValueError(
-                "Challenge did not pass for {0}: {1}".format(domain, authorization)
+                "Challenge did not pass for {}: {}".format(domain, authorization)
             )
         os.remove(wellknown_path)
-        log.info("{0} verified!".format(domain))
+        log.info("{} verified!".format(domain))
 
     # finalize the order with the csr
     log.info("Signing certificate...")
@@ -251,7 +251,7 @@ def get_crt(
         "Error checking order status",
     )
     if order["status"] != "valid":
-        raise ValueError("Order failed: {0}".format(order))
+        raise ValueError("Order failed: {}".format(order))
 
     # download the certificate
     certificate_pem, _, _ = _send_signed_request(
diff --git a/tests/test_translation_format_consistency.py b/tests/test_translation_format_consistency.py
index 86d1c3279..bfd0e3ae4 100644
--- a/tests/test_translation_format_consistency.py
+++ b/tests/test_translation_format_consistency.py
@@ -26,10 +26,10 @@ def find_inconsistencies(locale_file):
         # Then we check that every "{stuff}" (for python's .format())
         # should also be in the translated string, otherwise the .format
         # will trigger an exception!
-        subkeys_in_ref = set(k[0] for k in re.findall(r"{(\w+)(:\w)?}", string))
-        subkeys_in_this_locale = set(
+        subkeys_in_ref = {k[0] for k in re.findall(r"{(\w+)(:\w)?}", string)}
+        subkeys_in_this_locale = {
             k[0] for k in re.findall(r"{(\w+)(:\w)?}", this_locale[key])
-        )
+        }
 
         if any(k not in subkeys_in_ref for k in subkeys_in_this_locale):
             yield """\n