diff --git a/tools/apigen.py b/tools/apigen.py
index 9f40230d4..c25636c93 100644
--- a/tools/apigen.py
+++ b/tools/apigen.py
@@ -342,7 +342,7 @@ def discover_modules(self):
             root_uri = self._path2uri(os.path.join(self.root_path,
                                                    dirpath))
             for dirname in dirnames[:]: # copy list - we modify inplace
-                package_uri = '.'.join((root_uri, dirname))
+                package_uri = f'{root_uri}.{dirname}'
                 if (self._uri2path(package_uri) and
                     self._survives_exclude(package_uri, 'package')):
                     modules.append(package_uri)
@@ -351,7 +351,7 @@ def discover_modules(self):
             # Check filenames for modules
             for filename in filenames:
                 module_name = filename[:-3]
-                module_uri = '.'.join((root_uri, module_name))
+                module_uri = f'{root_uri}.{module_name}'
                 if (self._uri2path(module_uri) and
                     self._survives_exclude(module_uri, 'module')):
                     modules.append(module_uri)