diff --git a/vcsserver/hooks.py b/vcsserver/hooks.py
--- a/vcsserver/hooks.py
+++ b/vcsserver/hooks.py
@@ -633,7 +633,7 @@ def git_post_receive(unused_repo_path, r
                     branches.append(push_ref['name'])
 
                 cmd = [settings.GIT_EXECUTABLE, 'log',
-                       '{old_rev}..{new_rev}'.format(**push_ref),
+                       f'{push_ref["old_rev"]}..{push_ref["new_rev"]}',
                        '--reverse', '--pretty=format:%H']
                 stdout, stderr = subprocessio.run_command(
                     cmd, env=os.environ.copy())
diff --git a/vcsserver/utils.py b/vcsserver/utils.py
--- a/vcsserver/utils.py
+++ b/vcsserver/utils.py
@@ -41,8 +41,7 @@ class StrictAttributeDict(AttributeDictB
         try:
             return self[attr]
         except KeyError:
-            raise AttributeError('{} object has no attribute {}'.format(
-                self.__class__, attr))
+            raise AttributeError(f'{self.__class__} object has no attribute {attr}')
 
 
 class AttributeDict(AttributeDictBase):