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1.python的执行过程
1)对python源代码进行编译，产生字节码
2)将编译结果交给python虚拟机，由虚拟机按照顺序一条一条地执行字节码，产生执行结果
图7-1


2.Python编译器的编译结果——PyCodeObject对象
Python编译器的编译结果中包含了字符串、常量值、字节码等在源代码中出现的一切有用的静态信息。
在Python运行期间，这些静态信息被PyCodeObject对象中
在Python运行结束后，这些信息会被存储在pyc文件中
PyCodeObject对象和pyc文件是Python对源文件编译结果的两种不同存在形式


3.Python源码中的PyCodeObject

/* Bytecode object */
typedef struct {
    PyObject_HEAD
    int co_argcount;		/* 位置参数个数*/
    int co_nlocals;		/* 局部变量个数，包括位置参数个数*/
    int co_stacksize;		/* 需要的栈空间 */
    int co_flags;		/* CO_..., see below */
    PyObject *co_code;		/* 字节码指令序列，以PyStringObject形式存在 */
    PyObject *co_consts;	/* PyTupleObject对象，保存所有的常量 */
    PyObject *co_names;		/* PyTupleObject对象，保存所有符号 */
    PyObject *co_varnames;	/* 局部变量名集合 */
    PyObject *co_freevars;	/* 实现闭包需要用到的东西 */
    PyObject *co_cellvars;      /* 内部嵌套函数所引用的局部变量名集合 */
    /* The rest doesn't count for hash/cmp */
    PyObject *co_filename;	/* Code Block所对应的.py文件的完整路径 */
    PyObject *co_name;		/* Code Block的名字，通常是函数名或类名 */
    int co_firstlineno;		/* Code Block所对应的.py文件的起始行 */
    PyObject *co_lnotab;	/* 字节码指令与.py文件中source code行号的对应关系，以PyStringObject的等式存在 */
    void *co_zombieframe;     /* for optimization only (see frameobject.c) */
    PyObject *co_weakreflist;   /* to support weakrefs to code objects */
} PyCodeObject;

#会产生三个 PyCodeObject，分别对应整个文件，class A和 def Fun
class A:
	pass
def Fun():
	pass
a = A()
Fun()

static void w_object(PyObject *v, WFILE *p)
{
	//……
	else if (PyCode_Check(v))
	{
		PyCodeObject *co = (PyCodeObject *)v;
		w_byte(TYPE_CODE, p); 
		w_long(co->co_argcount, p);
		w_long(co->co_nlocals, p);
		w_long(co->co_stacksize, p);
		w_long(co->co_flags, p);
		w_object(co->co_code, p);
		w_object(co->co_consts, p);
		w_object(co->co_names, p);
		w_object(co->co_varnames, p);
		w_object(co->co_freevars, p);
		w_object(co->co_cellvars, p);
		w_object(co->co_filename, p);
		w_object(co->co_name, p);
		w_long(co->co_firstlineno, p);
		w_object(co->co_lnotab, p);
	}
	//…… 
}

typedef struct {
	FILE *fp;
	PyObject *strings; //在写入时指向dict，在读出时指向list
} WFILE;

//w_object对于字符串的处理
else if (PyString_CheckExact(v)) {
        if (p->strings && PyString_CHECK_INTERNED(v)) {
			//[1]：获得 PyStringObject对象在strings中的序号
            PyObject *o = PyDict_GetItem(p->strings, v);
			//[2]：intern字符串的非首次写入
            if (o) {
                long w = PyInt_AsLong(o);
                w_byte(TYPE_STRINGREF, p);
                w_long(w, p);
                goto exit;
            }
			//[3]：intern字符串的首次写入
            else {
                int ok;
                o = PyInt_FromSsize_t(PyDict_Size(p->strings));
                ok = o &&
                     PyDict_SetItem(p->strings, v, o) >= 0;
                Py_XDECREF(o);
                if (!ok) {
                    p->depth--;
                    p->error = WFERR_UNMARSHALLABLE;
                    return;
                }
                w_byte(TYPE_INTERNED, p);
            }
        }
		//[4]：写入普通字符串
        else {
            w_byte(TYPE_STRING, p);
        }
		//写入字符串
        w_pstring(PyBytes_AS_STRING(v), PyString_GET_SIZE(v), p);
}
//...

STOP_CODE() 
Indicates end-of-code to the compiler, not used by the interpreter.
NOP() 
Do nothing code. Used as a placeholder by the bytecode optimizer.
POP_TOP() 
Removes the top-of-stack (TOS) item.
ROT_TWO() 
Swaps the two top-most stack items.
ROT_THREE() 
Lifts second and third stack item one position up, moves top down to position three.
ROT_FOUR() 
Lifts second, third and forth stack item one position up, moves top down to position four.
//...