PEP 227 implementation

The majority of the changes are in the compiler.  The mainloop changes
primarily to implement the new opcodes and to pass a function's
closure to eval_code2().  Frames and functions got new slots to hold
the closure.

Include/compile.h
    Add co_freevars and co_cellvars slots to code objects.
    Update PyCode_New() to take freevars and cellvars as arguments
Include/funcobject.h
    Add func_closure slot to function objects.
    Add GetClosure()/SetClosure() functions (and corresponding
    macros) for getting at the closure.
Include/frameobject.h
    PyFrame_New() now takes a closure.
Include/opcode.h
    Add four new opcodes: MAKE_CLOSURE, LOAD_CLOSURE, LOAD_DEREF,
    STORE_DEREF.
    Remove comment about old requirement for opcodes to fit in 7
    bits.
compile.c
    Implement changes to code objects for co_freevars and co_cellvars.

    Modify symbol table to use st_cur_name (string object for the name
    of the current scope) and st_cur_children (list of nested blocks).
    Also define st_nested, which might more properly be called
    st_cur_nested.  Add several DEF_XXX flags to track def-use
    information for free variables.

    New or modified functions of note:
    com_make_closure(struct compiling *, PyCodeObject *)
        Emit LOAD_CLOSURE opcodes as needed to pass cells for free
        variables into nested scope.
    com_addop_varname(struct compiling *, int, char *)
        Emits opcodes for LOAD_DEREF and STORE_DEREF.
    get_ref_type(struct compiling *, char *name)
        Return NAME_CLOSURE if ref type is FREE or CELL
    symtable_load_symbols(struct compiling *)
        Decides what variables are cell or free based on def-use info.
        Can now raise SyntaxError if nested scopes are mixed with
        exec or from blah import *.
    make_scope_info(PyObject *, PyObject *, int, int)
        Helper functions for symtable scope stack.
    symtable_update_free_vars(struct symtable *)
        After a code block has been analyzed, it must check each of
        its children for free variables that are not defined in the
        block.  If a variable is free in a child and not defined in
        the parent, then it is defined by block the enclosing the
        current one or it is a global.  This does the right logic.
    symtable_add_use() is now a macro for symtable_add_def()
    symtable_assign(struct symtable *, node *)
        Use goto instead of for (;;)

    Fixed bug in symtable where name of keyword argument in function
    call was treated as assignment in the scope of the call site. Ex:
        def f():
            g(a=2) # a was considered a local of f

ceval.c
    eval_code2() now take one more argument, a closure.
    Implement LOAD_CLOSURE, LOAD_DEREF, STORE_DEREF, MAKE_CLOSURE>

    Also: When name error occurs for global variable, report that the
    name was global in the error mesage.

Objects/frameobject.c
    Initialize f_closure to be a tuple containing space for cellvars
    and freevars.  f_closure is NULL if neither are present.
Objects/funcobject.c
    Add support for func_closure.
Python/import.c
    Change the magic number.
Python/marshal.c
    Track changes to code objects.

Include/compile.h

@@ -18,6 +18,8 @@ typedef struct {
     PyObject *co_consts;	/* list (constants used) */
     PyObject *co_names;		/* list of strings (names used) */
     PyObject *co_varnames;	/* tuple of strings (local variable names) */
+    PyObject *co_freevars;	/* tuple of strings (free variable names) */
+    PyObject *co_cellvars;      /* tuple of strings (cell variable names) */
     /* The rest doesn't count for hash/cmp */
     PyObject *co_filename;	/* string (where it was loaded from) */
     PyObject *co_name;		/* string (name, for reference) */
@@ -42,7 +44,8 @@ struct _node; /* Declare the existence of this type */
 DL_IMPORT(PyCodeObject *) PyNode_Compile(struct _node *, char *);
 DL_IMPORT(PyCodeObject *) PyCode_New(
 	int, int, int, int, PyObject *, PyObject *, PyObject *, PyObject *,
-	PyObject *, PyObject *, int, PyObject *); /* same as struct above */
+	PyObject *, PyObject *, PyObject *, PyObject *, int, PyObject *); 
+        /* same as struct above */
 DL_IMPORT(int) PyCode_Addr2Line(PyCodeObject *, int);
 
 /* for internal use only */

Include/frameobject.h

@@ -20,6 +20,7 @@ typedef struct _frame {
     PyObject *f_builtins;	/* builtin symbol table (PyDictObject) */
     PyObject *f_globals;	/* global symbol table (PyDictObject) */
     PyObject *f_locals;		/* local symbol table (PyDictObject) */
+    PyObject *f_closure;        /* environment for free variables */
     PyObject **f_valuestack;	/* points after the last local */
     PyObject *f_trace;		/* Trace function */
     PyObject *f_exc_type, *f_exc_value, *f_exc_traceback;
@@ -43,7 +44,8 @@ extern DL_IMPORT(PyTypeObject) PyFrame_Type;
 #define PyFrame_Check(op) ((op)->ob_type == &PyFrame_Type)
 
 DL_IMPORT(PyFrameObject *) PyFrame_New(PyThreadState *, PyCodeObject *,
-                                       PyObject *, PyObject *);
+                                       PyObject *, PyObject *,
+				       PyObject *);
 
 
 /* The rest of the interface is specific for frame objects */

Include/funcobject.h

@@ -12,6 +12,7 @@ typedef struct {
     PyObject *func_code;
     PyObject *func_globals;
     PyObject *func_defaults;
+    PyObject *func_closure;
     PyObject *func_doc;
     PyObject *func_name;
     PyObject *func_dict;
@@ -26,6 +27,8 @@ extern DL_IMPORT(PyObject *) PyFunction_GetCode(PyObject *);
 extern DL_IMPORT(PyObject *) PyFunction_GetGlobals(PyObject *);
 extern DL_IMPORT(PyObject *) PyFunction_GetDefaults(PyObject *);
 extern DL_IMPORT(int) PyFunction_SetDefaults(PyObject *, PyObject *);
+extern DL_IMPORT(PyObject *) PyFunction_GetClosure(PyObject *);
+extern DL_IMPORT(int) PyFunction_SetClosure(PyObject *, PyObject *);
 
 /* Macros for direct access to these values. Type checks are *not*
    done, so use with care. */
@@ -35,6 +38,8 @@ extern DL_IMPORT(int) PyFunction_SetDefaults(PyObject *, PyObject *);
 	(((PyFunctionObject *)func) -> func_globals)
 #define PyFunction_GET_DEFAULTS(func) \
 	(((PyFunctionObject *)func) -> func_defaults)
+#define PyFunction_GET_CLOSURE(func) \
+	(((PyFunctionObject *)func) -> func_closure)
 
 #ifdef __cplusplus
 }

Include/opcode.h

@@ -114,17 +114,17 @@ extern "C" {
 
 #define SET_LINENO	127	/* Current line number */
 
-/* It used to be the case that opcodes should fit in 7 bits.  This is
-   no longer the case -- 8 bits is fine (the instruction stream is now
-   a sequence of unsigned characters).  We gladly use the new space
-   for new opcodes. */
-
 #define RAISE_VARARGS	130	/* Number of raise arguments (1, 2 or 3) */
 /* CALL_FUNCTION_XXX opcodes defined below depend on this definition */
 #define CALL_FUNCTION	131	/* #args + (#kwargs<<8) */
 #define MAKE_FUNCTION	132	/* #defaults */
 #define BUILD_SLICE 	133	/* Number of items */
 
+#define MAKE_CLOSURE    134     /* #free vars */
+#define LOAD_CLOSURE    135     /* Load free variable from closure */
+#define LOAD_DEREF      136     /* Load and dereference from closure cell */ 
+#define STORE_DEREF     137     /* Store into cell */ 
+
 /* The next 3 opcodes must be contiguous and satisfy
    (CALL_FUNCTION_VAR - CALL_FUNCTION) & 3 == 1  */
 #define CALL_FUNCTION_VAR          140	/* #args + (#kwargs<<8) */