Refactor as 'bypass_when' and 'bypass_unless' because one is likely m…

…uch more useful to the caller than the other.

CHANGES.rst

@@ -1,7 +1,7 @@
 v3.7.0
 ======
 
-Added ``bypass_unless``.
+Added ``bypass_unless`` and ``bypass_when`` and ``identity``.
 
 v3.6.0
 ======

jaraco/functools.py

@@ -1,9 +1,10 @@
+import collections
 import functools
-import time
 import inspect
-import collections
-import types
 import itertools
+import operator
+import time
+import types
 import warnings
 
 import more_itertools
@@ -556,27 +557,49 @@ def wrapper(*args, **kwargs):
     return decorate
 
 
-def bypass_unless(check):
+def identity(x):
+    return x
+
+
+def bypass_when(check, *, _op=identity):
     """
-    Decorate a function to return its parameter unless ``check``.
+    Decorate a function to return its parameter when ``check``.
 
-    >>> enabled = [object()]  # True
+    >>> bypassed = []  # False
 
-    >>> @bypass_unless(enabled)
+    >>> @bypass_when(bypassed)
     ... def double(x):
     ...     return x * 2
     >>> double(2)
     4
-    >>> del enabled[:]  # False
+    >>> bypassed[:] = [object()]  # True
     >>> double(2)
     2
     """
 
     def decorate(func):
         @functools.wraps(func)
         def wrapper(param):
-            return func(param) if check else param
+            return param if _op(check) else func(param)
 
         return wrapper
 
     return decorate
+
+
+def bypass_unless(check):
+    """
+    Decorate a function to return its parameter unless ``check``.
+
+    >>> enabled = [object()]  # True
+
+    >>> @bypass_unless(enabled)
+    ... def double(x):
+    ...     return x * 2
+    >>> double(2)
+    4
+    >>> del enabled[:]  # False
+    >>> double(2)
+    2
+    """
+    return bypass_when(check, _op=operator.not_)