diff --git a/moulinette/actionsmap.py b/moulinette/actionsmap.py
index 386018ec..b0b4b2bc 100644
--- a/moulinette/actionsmap.py
+++ b/moulinette/actionsmap.py
@@ -410,7 +410,7 @@ class ActionsMap(object):
         for n in self.get_namespaces():
             logger.debug("loading actions map namespace '%s'", n)
 
-            actionsmap_yml = "%s/actionsmap/%s.yml" % (DATA_DIR, n)
+            actionsmap_yml = "{}/actionsmap/{}.yml".format(DATA_DIR, n)
             actionsmap_yml_stat = os.stat(actionsmap_yml)
             actionsmap_pkl = "%s/actionsmap/%s-%d-%d.pkl" % (
                 CACHE_DIR,
@@ -428,7 +428,7 @@ class ActionsMap(object):
                 actionsmap = read_yaml(actionsmap_yml)
 
                 # Delete old cache files
-                for old_cache in glob.glob("%s/actionsmap/%s-*.pkl" % (CACHE_DIR, n)):
+                for old_cache in glob.glob("{}/actionsmap/{}-*.pkl".format(CACHE_DIR, n)):
                     os.remove(old_cache)
 
                 # at installation, cachedir might not exists
@@ -479,7 +479,7 @@ class ActionsMap(object):
             auth_method = self.default_authentication
 
         # Load and initialize the authenticator module
-        auth_module = "%s.authenticators.%s" % (self.main_namespace, auth_method)
+        auth_module = "{}.authenticators.{}".format(self.main_namespace, auth_method)
         logger.debug(f"Loading auth module {auth_module}")
         try:
             mod = import_module(auth_module)
@@ -532,12 +532,12 @@ class ActionsMap(object):
         # Retrieve action information
         if len(tid) == 4:
             namespace, category, subcategory, action = tid
-            func_name = "%s_%s_%s" % (
+            func_name = "{}_{}_{}".format(
                 category,
                 subcategory.replace("-", "_"),
                 action.replace("-", "_"),
             )
-            full_action_name = "%s.%s.%s.%s" % (
+            full_action_name = "{}.{}.{}.{}".format(
                 namespace,
                 category,
                 subcategory,
@@ -547,22 +547,22 @@ class ActionsMap(object):
             assert len(tid) == 3
             namespace, category, action = tid
             subcategory = None
-            func_name = "%s_%s" % (category, action.replace("-", "_"))
-            full_action_name = "%s.%s.%s" % (namespace, category, action)
+            func_name = "{}_{}".format(category, action.replace("-", "_"))
+            full_action_name = "{}.{}.{}".format(namespace, category, action)
 
         # Lock the moulinette for the namespace
         with MoulinetteLock(namespace, timeout):
             start = time()
             try:
                 mod = __import__(
-                    "%s.%s" % (namespace, category),
+                    "{}.{}".format(namespace, category),
                     globals=globals(),
                     level=0,
                     fromlist=[func_name],
                 )
                 logger.debug(
                     "loading python module %s took %.3fs",
-                    "%s.%s" % (namespace, category),
+                    "{}.{}".format(namespace, category),
                     time() - start,
                 )
                 func = getattr(mod, func_name)
@@ -570,7 +570,7 @@ class ActionsMap(object):
                 import traceback
 
                 traceback.print_exc()
-                error_message = "unable to load function %s.%s because: %s" % (
+                error_message = "unable to load function {}.{} because: {}".format(
                     namespace,
                     func_name,
                     e,
@@ -619,7 +619,7 @@ class ActionsMap(object):
         # Look for all files that match the given patterns in the actionsmap dir
         for namespace_pattern in NAMESPACE_PATTERNS:
             namespaces.extend(
-                glob.glob("%s/actionsmap/%s.yml" % (DATA_DIR, namespace_pattern))
+                glob.glob("{}/actionsmap/{}.yml".format(DATA_DIR, namespace_pattern))
             )
 
         # Keep only the filenames with extension
diff --git a/moulinette/core.py b/moulinette/core.py
index 6f6fddd7..9dfcd7f8 100644
--- a/moulinette/core.py
+++ b/moulinette/core.py
@@ -230,7 +230,7 @@ class Moulinette18n(object):
             # Create new Translator object
             lib_dir = env["LIB_DIR"]
             translator = Translator(
-                "%s/%s/locales" % (lib_dir, namespace), self.default_locale
+                "{}/{}/locales".format(lib_dir, namespace), self.default_locale
             )
             translator.set_locale(self.locale)
             self._namespaces[namespace] = translator
diff --git a/moulinette/interfaces/__init__.py b/moulinette/interfaces/__init__.py
index d8bed853..9a5a353a 100644
--- a/moulinette/interfaces/__init__.py
+++ b/moulinette/interfaces/__init__.py
@@ -211,7 +211,7 @@ class _CallbackAction(argparse.Action):
             import traceback
 
             traceback.print_exc()
-            raise ValueError("unable to import method {0}".format(self.callback_method))
+            raise ValueError("unable to import method {}".format(self.callback_method))
         self._callback = func
 
     def __call__(self, parser, namespace, values, option_string=None):
@@ -226,7 +226,7 @@ class _CallbackAction(argparse.Action):
         except Exception as e:
             error_message = (
                 "cannot get value from callback method "
-                "'{0}': {1}".format(self.callback_method, e)
+                "'{}': {}".format(self.callback_method, e)
             )
             logger.exception(error_message)
             raise MoulinetteError(error_message, raw_msg=True)
@@ -562,7 +562,7 @@ class PositionalsFirstHelpFormatter(argparse.HelpFormatter):
                 usage = "\n".join(lines)
 
         # prefix with 'usage:'
-        return "%s%s\n\n" % (prefix, usage)
+        return "{}{}\n\n".format(prefix, usage)
 
 
 class JSONExtendedEncoder(JSONEncoder):
diff --git a/moulinette/interfaces/api.py b/moulinette/interfaces/api.py
index 7be0c3b4..4bfc51fe 100644
--- a/moulinette/interfaces/api.py
+++ b/moulinette/interfaces/api.py
@@ -38,9 +38,9 @@ logger = log.getLogger("moulinette.interface.api")
 # We define a global variable to manage in a dirty way the upload...
 UPLOAD_DIR = None
 
-CSRF_TYPES = set(
-    ["text/plain", "application/x-www-form-urlencoded", "multipart/form-data"]
-)
+CSRF_TYPES = {
+    "text/plain", "application/x-www-form-urlencoded", "multipart/form-data"
+}
 
 
 def is_csrf():
@@ -667,7 +667,7 @@ class ActionsMapParser(BaseActionsMapParser):
             # Retrieve the tid for the route
             _, parser = self._parsers[route]
         except KeyError as e:
-            error_message = "no argument parser found for route '%s': %s" % (route, e)
+            error_message = "no argument parser found for route '{}': {}".format(route, e)
             logger.error(error_message)
             raise MoulinetteValidationError(error_message, raw_msg=True)
 
@@ -684,7 +684,7 @@ class ActionsMapParser(BaseActionsMapParser):
             # Retrieve the parser for the route
             _, parser = self._parsers[route]
         except KeyError as e:
-            error_message = "no argument parser found for route '%s': %s" % (route, e)
+            error_message = "no argument parser found for route '{}': {}".format(route, e)
             logger.error(error_message)
             raise MoulinetteValidationError(error_message, raw_msg=True)
         ret = argparse.Namespace()
diff --git a/moulinette/interfaces/cli.py b/moulinette/interfaces/cli.py
index a27f5dc1..4ad659a0 100644
--- a/moulinette/interfaces/cli.py
+++ b/moulinette/interfaces/cli.py
@@ -251,7 +251,7 @@ class TTYHandler(logging.StreamHandler):
                 # add translated level name before message
                 level = "%s " % m18n.g(record.levelname.lower())
             color = self.LEVELS_COLOR.get(record.levelno, "white")
-            msg = "{0}{1}{2}{3}".format(colors_codes[color], level, END_CLI_COLOR, msg)
+            msg = "{}{}{}{}".format(colors_codes[color], level, END_CLI_COLOR, msg)
         if self.formatter:
             # use user-defined formatter
             record.__dict__[self.message_key] = msg
@@ -403,7 +403,7 @@ class ActionsMapParser(BaseActionsMapParser):
         except SystemExit:
             raise
         except Exception as e:
-            error_message = "unable to parse arguments '%s' because: %s" % (
+            error_message = "unable to parse arguments '{}' because: {}".format(
                 " ".join(args),
                 e,
             )
@@ -435,7 +435,7 @@ class ActionsMapParser(BaseActionsMapParser):
         except SystemExit:
             raise
         except Exception as e:
-            error_message = "unable to parse arguments '%s' because: %s" % (
+            error_message = "unable to parse arguments '{}' because: {}".format(
                 " ".join(args),
                 e,
             )
diff --git a/moulinette/utils/filesystem.py b/moulinette/utils/filesystem.py
index 208987a8..36a447ba 100644
--- a/moulinette/utils/filesystem.py
+++ b/moulinette/utils/filesystem.py
@@ -24,7 +24,7 @@ def read_file(file_path, file_mode="r"):
     """
     assert isinstance(
         file_path, str
-    ), "Error: file_path '%s' should be a string but is of type '%s' instead" % (
+    ), "Error: file_path '{}' should be a string but is of type '{}' instead".format(
         file_path,
         type(file_path),
     )
@@ -121,7 +121,7 @@ def write_to_file(file_path, data, file_mode="w"):
     """
     assert (
         isinstance(data, str) or isinstance(data, bytes) or isinstance(data, list)
-    ), "Error: data '%s' should be either a string or a list but is of type '%s'" % (
+    ), "Error: data '{}' should be either a string or a list but is of type '{}'".format(
         data,
         type(data),
     )
@@ -130,7 +130,7 @@ def write_to_file(file_path, data, file_mode="w"):
     )
     assert os.path.isdir(
         os.path.dirname(file_path)
-    ), "Error: the path ('%s') base dir ('%s') is not a dir" % (
+    ), "Error: the path ('{}') base dir ('{}') is not a dir".format(
         file_path,
         os.path.dirname(file_path),
     )
@@ -140,7 +140,7 @@ def write_to_file(file_path, data, file_mode="w"):
         for element in data:
             assert isinstance(
                 element, str
-            ), "Error: element '%s' should be a string but is of type '%s' instead" % (
+            ), "Error: element '{}' should be a string but is of type '{}' instead".format(
                 element,
                 type(element),
             )
@@ -179,13 +179,13 @@ def write_to_json(file_path, data, sort_keys=False, indent=None):
     # Assumptions
     assert isinstance(
         file_path, str
-    ), "Error: file_path '%s' should be a string but is of type '%s' instead" % (
+    ), "Error: file_path '{}' should be a string but is of type '{}' instead".format(
         file_path,
         type(file_path),
     )
     assert isinstance(data, dict) or isinstance(
         data, list
-    ), "Error: data '%s' should be a dict or a list but is of type '%s' instead" % (
+    ), "Error: data '{}' should be a dict or a list but is of type '{}' instead".format(
         data,
         type(data),
     )
@@ -194,7 +194,7 @@ def write_to_json(file_path, data, sort_keys=False, indent=None):
     )
     assert os.path.isdir(
         os.path.dirname(file_path)
-    ), "Error: the path ('%s') base dir ('%s') is not a dir" % (
+    ), "Error: the path ('{}') base dir ('{}') is not a dir".format(
         file_path,
         os.path.dirname(file_path),
     )
diff --git a/moulinette/utils/text.py b/moulinette/utils/text.py
index 8e959a78..2da101a5 100644
--- a/moulinette/utils/text.py
+++ b/moulinette/utils/text.py
@@ -59,7 +59,7 @@ def searchf(pattern, path, count=0, flags=re.MULTILINE):
 def prependlines(text, prepend):
     """Prepend a string to each line of a text"""
     lines = text.splitlines(True)
-    return "%s%s" % (prepend, prepend.join(lines))
+    return "{}{}".format(prepend, prepend.join(lines))
 
 
 # Randomize ------------------------------------------------------------
diff --git a/test/conftest.py b/test/conftest.py
index d40e1116..51ea6f33 100644
--- a/test/conftest.py
+++ b/test/conftest.py
@@ -40,7 +40,7 @@ def patch_translate(moulinette):
 
 def patch_logging(moulinette):
     """Configure logging to use the custom logger."""
-    handlers = set(["tty", "api"])
+    handlers = {"tty", "api"}
     root_handlers = set(handlers)
 
     level = "INFO"
@@ -97,8 +97,8 @@ def moulinette(tmp_path_factory):
     moulinette.env["DATA_DIR"] = tmp_data
     moulinette.env["LIB_DIR"] = tmp_lib
     shutil.copytree("./test/actionsmap", "%s/actionsmap" % tmp_data)
-    shutil.copytree("./test/src", "%s/%s" % (tmp_lib, namespace))
-    shutil.copytree("./test/locales", "%s/%s/locales" % (tmp_lib, namespace))
+    shutil.copytree("./test/src", "{}/{}".format(tmp_lib, namespace))
+    shutil.copytree("./test/locales", "{}/{}/locales".format(tmp_lib, namespace))
 
     patch_init(moulinette)
     patch_translate(moulinette)
diff --git a/test/test_actionsmap.py b/test/test_actionsmap.py
index 0abdd7f4..87f7ae17 100644
--- a/test/test_actionsmap.py
+++ b/test/test_actionsmap.py
@@ -192,7 +192,7 @@ def test_extra_argument_parser_add_argument_bad_arg(iface):
     with pytest.raises(MoulinetteError) as exception:
         extra_argument_parse.add_argument("_global", "foo", {"ask": 1})
 
-    expected_msg = "unable to validate extra parameter '%s' for argument '%s': %s" % (
+    expected_msg = "unable to validate extra parameter '{}' for argument '{}': {}".format(
         "ask",
         "foo",
         "parameter value must be a string, got 1",
@@ -266,7 +266,7 @@ def test_actions_map_import_error(mocker):
     with pytest.raises(MoulinetteError) as exception:
         amap.process({}, timeout=30, route=("GET", "/test-auth/none"))
 
-    expected_msg = "unable to load function % s.%s because: %s" % (
+    expected_msg = "unable to load function {: }.{} because: {}".format(
         "moulitest",
         "testauth_none",
         "Yoloswag",
diff --git a/test/test_i18n_format_consistency.py b/test/test_i18n_format_consistency.py
index 86d1c327..bfd0e3ae 100644
--- a/test/test_i18n_format_consistency.py
+++ b/test/test_i18n_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
diff --git a/test/test_serialize.py b/test/test_serialize.py
index 0935967b..d3901bb7 100644
--- a/test/test_serialize.py
+++ b/test/test_serialize.py
@@ -5,7 +5,7 @@ from moulinette.interfaces import JSONExtendedEncoder
 def test_json_extended_encoder(caplog):
     encoder = JSONExtendedEncoder()
 
-    assert encoder.default(set([1, 2, 3])) == [1, 2, 3]
+    assert encoder.default({1, 2, 3}) == [1, 2, 3]
 
     assert encoder.default(dt(1917, 3, 8)) == "1917-03-08T00:00:00+00:00"
 
diff --git a/test/test_translation_format_consistency.py b/test/test_translation_format_consistency.py
index 86d1c327..bfd0e3ae 100644
--- a/test/test_translation_format_consistency.py
+++ b/test/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