argparse docs: prog default is the basename of argv[0] (GH-30298) (GH-30339)

diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst
index a056826..d853d2a 100644
--- a/Doc/library/argparse.rst
+++ b/Doc/library/argparse.rst
@@ -148,7 +148,8 @@
    as keyword arguments. Each parameter has its own more detailed description
    below, but in short they are:
 
-   * prog_ - The name of the program (default: ``sys.argv[0]``)
+   * prog_ - The name of the program (default:
+     ``os.path.basename(sys.argv[0])``)
 
    * usage_ - The string describing the program usage (default: generated from
      arguments added to parser)
diff --git a/Lib/argparse.py b/Lib/argparse.py
index b2db312..e177e4f 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1672,7 +1672,8 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
     """Object for parsing command line strings into Python objects.
 
     Keyword Arguments:
-        - prog -- The name of the program (default: sys.argv[0])
+        - prog -- The name of the program (default:
+            ``os.path.basename(sys.argv[0])``)
         - usage -- A usage message (default: auto-generated from arguments)
         - description -- A description of what the program does
         - epilog -- Text following the argument descriptions