diff --git a/doc/en/example/nonpython/conftest.py b/doc/en/example/nonpython/conftest.py
index 525d2b623..e969e3e25 100644
--- a/doc/en/example/nonpython/conftest.py
+++ b/doc/en/example/nonpython/conftest.py
@@ -12,7 +12,7 @@ class YamlFile(pytest.File):
         # We need a yaml parser, e.g. PyYAML.
         import yaml
 
-        raw = yaml.safe_load(self.path.open(encoding='utf-8'))
+        raw = yaml.safe_load(self.path.open(encoding="utf-8"))
         for name, spec in sorted(raw.items()):
             yield YamlItem.from_parent(self, name=name, spec=spec)