[3.7] bpo-26806: add 30 to the recursion limit in IDLE's shell (GH-13944)

Doc/library/idle.rst

@@ -713,6 +713,10 @@ or ``print`` or ``write`` to sys.stdout or sys.stderr,
 IDLE should be started in a command line window.  The secondary subprocess
 will then be attached to that window for input and output.
 
+The IDLE code running in the execution process adds frames to the call stack
+that would not be there otherwise.  IDLE wraps ``sys.getrecursionlimit`` and
+``sys.setrecursionlimit`` to reduce the effect of the additional stack frames.
+
 If ``sys`` is reset by user code, such as with ``importlib.reload(sys)``,
 IDLE's changes are lost and input from the keyboard and output to the screen
 will not work correctly.

Lib/idlelib/NEWS.txt

@@ -3,6 +3,11 @@ Released on 2019-06-24?
 ======================================
 
 
+bpo-26806: To compensate for stack frames added by IDLE and avoid
+possible problems with low recursion limits, add 30 to limits in the
+user code execution process.  Subtract 30 when reporting recursion
+limits to make this addition mostly transparent.
+
 bpo-37325: Fix tab focus traversal order for help source and custom
 run dialogs.