Fix parameter names in assertIn() docs (GH-18829)

The names "member" and "container" for the arguments are also used in the module and shown with the help() function, and are immediately understandable in this context, contrary to "first" and "second".

diff --git a/Doc/library/unittest.rst b/Doc/library/unittest.rst
index e2e4f2cdc220aa10dbe1bd04f440a43c86a0d272..b2e16cf331e036ceb192421a0931a04970582ff4 100644 (file)
--- a/Doc/library/unittest.rst
+++ b/Doc/library/unittest.rst
@@ -910,10 +910,10 @@ Test cases
       .. versionadded:: 3.1
 
 
-   .. method:: assertIn(first, second, msg=None)
-               assertNotIn(first, second, msg=None)
+   .. method:: assertIn(member, container, msg=None)
+               assertNotIn(member, container, msg=None)
 
-      Test that *first* is (or is not) in *second*.
+      Test that *member* is (or is not) in *container*.
 
       .. versionadded:: 3.1