Issue #20226: Major improvements to Argument Clinic.

* You may now specify an expression as the default value for a
  parameter!  Example: "sys.maxsize - 1".  This support is
  intentionally quite limited; you may only use values that
  can be represented as static C values.
* Removed "doc_default", simplified support for "c_default"
  and "py_default".  (I'm not sure we still even need
  "py_default", but I'm leaving it in for now in case a
  use presents itself.)
* Parameter lines support a trailing '\\' as a line
  continuation character, allowing you to break up long lines.
* The argument parsing code generated when supporting optional
  groups now uses PyTuple_GET_SIZE instead of PyTuple_GetSize,
  leading to a 850% speedup in parsing.  (Just kidding, this
  is an unmeasurable difference.)
* A bugfix for the recent regression where the generated
  prototype from pydoc for builtins would be littered with
  unreadable "=<object ...>"" default values for parameters
  that had no default value.
* Converted some asserts into proper failure messages.
* Many doc improvements and fixes.
diff --git a/Modules/_opcode.c b/Modules/_opcode.c
index fe7f8ab..2e84699 100644
--- a/Modules/_opcode.c
+++ b/Modules/_opcode.c
@@ -39,7 +39,7 @@
     int oparg = 0;
     int _return_value;
 
-    switch (PyTuple_Size(args)) {
+    switch (PyTuple_GET_SIZE(args)) {
         case 1:
             if (!PyArg_ParseTuple(args, "i:stack_effect", &opcode))
                 return NULL;
@@ -64,7 +64,7 @@
 
 static int
 _opcode_stack_effect_impl(PyModuleDef *module, int opcode, int group_right_1, int oparg)
-/*[clinic end generated code: checksum=e880e62dc7b0de73403026eaf4f8074aa106358b]*/
+/*[clinic end generated code: checksum=47e76ec27523da4ab192713642d32482cd743aa4]*/
 {
     int effect;
     if (HAS_ARG(opcode)) {