Refactor membership test

idna/core.py

diff --git a/idna/core.py b/idna/core.py
index 0678bd4..d303b38 100644
--- a/idna/core.py
+++ b/idna/core.py
@@ -381,7 +381,7 @@
             status = uts46row[1]
             replacement: Optional[str] = None
             if std3_rules and code_point <= 0x7F:
-                if not code_point in _ldh:
+                if code_point not in _ldh:
                     raise InvalidCodepoint(
                         "Codepoint {} at position {} does not follow STD3 rules".format(_unot(code_point), pos + 1)
                     )