update comments

diff --git a/Python/ceval.c b/Python/ceval.c
index 24e41689ade9681cbe44cd000b1d13bde9dfeaf3..a42a66559b8a945c605089b379e592acc4fd48db 100644 (file)
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2491,20 +2491,23 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
                           - (TOP, SECOND) = (WHY_{RETURN,CONTINUE}), retval
                           - TOP = WHY_*; no retval below it
                           - (TOP, SECOND, THIRD) = exc_info()
+                            (FOURTH, FITH, SIXTH) = previous exception for EXCEPT_HANDLER
                           Below them is EXIT, the context.__exit__ bound method.
                           In the last case, we must call
                             EXIT(TOP, SECOND, THIRD)
                           otherwise we must call
                             EXIT(None, None, None)
 
-                          In all cases, we remove EXIT from the stack, leaving
-                          the rest in the same order.
+                          In the first two cases, we remove EXIT from the
+                          stack, leaving the rest in the same order.  In the
+                          third case, we shift the bottom 3 values of the
+                          stack down, and replace the empty spot with NULL.
 
                           In addition, if the stack represents an exception,
                           *and* the function call returns a 'true' value, we
-                          "zap" this information, to prevent END_FINALLY from
-                          re-raising the exception.  (But non-local gotos
-                          should still be resumed.)
+                          push WHY_SILENCED onto the stack.  END_FINALLY will
+                          then not re-raise the exception.  (But non-local
+                          gotos should still be resumed.)
                        */
 
                        PyObject *exit_func;
@@ -2544,7 +2547,11 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
                                stack_pointer[-7] = tb;
                                stack_pointer[-6] = exc;
                                stack_pointer[-5] = tp;
+                               /* UNWIND_EXCEPT_BLOCK will pop this off. */
                                FOURTH() = NULL;
+                               /* We just shifted the stack down, so we have
+                                  to tell the except handler block that the
+                                  values are lower than it expects. */
                                block = &f->f_blockstack[f->f_iblock - 1];
                                assert(block->b_type == EXCEPT_HANDLER);
                                block->b_level--;