bpo-10049: Add a "no-op" (null) context manager to contextlib (GH-4464)
Adds a simpler and faster alternative to ExitStack for handling
single optional context managers without having to change the
lexical structure of your code.
diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index 962ceda..c1f8a84 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -5,7 +5,7 @@
from collections import deque
from functools import wraps
-__all__ = ["asynccontextmanager", "contextmanager", "closing",
+__all__ = ["asynccontextmanager", "contextmanager", "closing", "nullcontext",
"AbstractContextManager", "ContextDecorator", "ExitStack",
"redirect_stdout", "redirect_stderr", "suppress"]
@@ -469,3 +469,24 @@
exc_details[1].__context__ = fixed_ctx
raise
return received_exc and suppressed_exc
+
+
+class nullcontext(AbstractContextManager):
+ """Context manager that does no additional processing.
+
+ Used as a stand-in for a normal context manager, when a particular
+ block of code is only sometimes used with a normal context manager:
+
+ cm = optional_cm if condition else nullcontext()
+ with cm:
+ # Perform operation, using optional_cm if condition is True
+ """
+
+ def __init__(self, enter_result=None):
+ self.enter_result = enter_result
+
+ def __enter__(self):
+ return self.enter_result
+
+ def __exit__(self, *excinfo):
+ pass