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‎.gitignore‎

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11
.DS_Store
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*.py[co]
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.ipynb_checkpoints/

‎ch11.md‎

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# Python虚拟机中的函数机制
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# Python 虚拟机中的函数机制
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一个函数意味着一个新的作用域（命名空间），当 Python 虚拟机执行一个函数时，首先创建一个 PyFrameObject，然后执行函数的字节码（PyCodeObject）。
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PyFunctionObject 的定义：
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```C
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typedef struct {
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PyObject_HEAD
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PyObject *func_code; /* A code object */
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PyObject *func_globals; /* A dictionary (other mappings won't do) */
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PyObject *func_defaults; /* NULL or a tuple */
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PyObject *func_closure; /* NULL or a tuple of cell objects */
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PyObject *func_doc; /* The __doc__ attribute, can be anything */
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PyObject *func_name; /* The __name__ attribute, a string object */
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PyObject *func_dict; /* The __dict__ attribute, a dict or NULL */
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PyObject *func_weakreflist; /* List of weak references */
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PyObject *func_module; /* The __module__ attribute, can be anything */
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/* Invariant:
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* func_closure contains the bindings for func_code->co_freevars, so
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* PyTuple_Size(func_closure) == PyCode_GetNumFree(func_code)
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* (func_closure may be NULL if PyCode_GetNumFree(func_code) == 0).
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*/
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} PyFunctionObject;
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```
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PyCodeObject 是在编译时产生的，包含函数的一些静态信息，如 co_consts, co_names, co_code 等，而 PyFunctionObject 则是执行 def 语句时动态产生的，包含 PyCodeObject 以及其它动态的信息，如 func_globals。
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一个函数只有一个 PyCodeObject，但是却会产生多个 PyFunctionObject，每次调用函数时都会创建一个新的 PyFunctionObject，该 PyFunctionObject 关联至唯一的 PyCodeObject。
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## 函数调用流程
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```python
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[func_0.py]
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def f():
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0 LOAD_CONST 0 (code object f)
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3 MAKE_FUNCTION 0
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6 STORE_NAME 0 (f)
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print "Function"
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0 LOAD_CONST 1 (“Function”)
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3 PRINT_ITEM
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4 PRINT_NEWLINE
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5 LOAD_CONST 0 (None)
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8 RETURN_VALUE
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f()
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9 LOAD_NAME 0 (f)
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12 CALL_FUNCTION 0
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15 POP_TOP
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16 LOAD_CONST 1 (None)
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19 RETURN_VALUE
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```
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重点指令：MAKE_FUNCTION，CALL_FUNCTION。
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```C
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case MAKE_FUNCTION:
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v = POP(); /* code object */
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x = PyFunction_New(v, f->f_globals);
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Py_DECREF(v);
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/* XXX Maybe this should be a separate opcode? */
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if (x != NULL && oparg> 0) {
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// oparg 表示 “具有默认值的参数” 的个数
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v = PyTuple_New(oparg);
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if (v == NULL) {
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Py_DECREF(x);
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x = NULL;
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break;
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}
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while (--oparg>= 0) {
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w = POP();
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PyTuple_SET_ITEM(v, oparg, w);
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}
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err = PyFunction_SetDefaults(x, v);
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Py_DECREF(v);
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}
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PUSH(x);
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break;
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```
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```C
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case CALL_FUNCTION:
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{
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PyObject **sp;
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PCALL(PCALL_ALL);
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sp = stack_pointer;
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#ifdef WITH_TSC
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x = call_function(&sp, oparg, &intr0, &intr1);
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#else
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x = call_function(&sp, oparg);
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#endif
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stack_pointer = sp;
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PUSH(x); // 函数返回值
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if (x != NULL)
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continue;
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break;
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}
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static PyObject *
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call_function(PyObject ***pp_stack, int oparg
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#ifdef WITH_TSC
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, uint64* pintr0, uint64* pintr1
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#endif
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)
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{
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// oparg 是 short 类型，高字节表示 nk（实参中关键字参数个数），低字节表示 na（实参中位置参数个数）
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int na = oparg & 0xff;
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int nk = (oparg>>8) & 0xff;
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int n = na + 2 * nk;
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PyObject **pfunc = (*pp_stack) - n - 1;
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PyObject *func = *pfunc;
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PyObject *x, *w;
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/* Always dispatch PyCFunction first, because these are
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presumed to be the most frequent callable object.
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*/
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if (PyCFunction_Check(func) && nk == 0) {
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int flags = PyCFunction_GET_FLAGS(func);
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PyThreadState *tstate = PyThreadState_GET();
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PCALL(PCALL_CFUNCTION);
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if (flags & (METH_NOARGS | METH_O)) {
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PyCFunction meth = PyCFunction_GET_FUNCTION(func);
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PyObject *self = PyCFunction_GET_SELF(func);
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if (flags & METH_NOARGS && na == 0) {
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C_TRACE(x, (*meth)(self,NULL));
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}
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else if (flags & METH_O && na == 1) {
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PyObject *arg = EXT_POP(*pp_stack);
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C_TRACE(x, (*meth)(self,arg));
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Py_DECREF(arg);
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}
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else {
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err_args(func, flags, na);
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x = NULL;
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}
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}
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else {
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PyObject *callargs;
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callargs = load_args(pp_stack, na);
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READ_TIMESTAMP(*pintr0);
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C_TRACE(x, PyCFunction_Call(func,callargs,NULL));
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READ_TIMESTAMP(*pintr1);
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Py_XDECREF(callargs);
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}
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} else {
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if (PyMethod_Check(func) && PyMethod_GET_SELF(func) != NULL) {
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/* optimize access to bound methods */
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PyObject *self = PyMethod_GET_SELF(func);
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PCALL(PCALL_METHOD);
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PCALL(PCALL_BOUND_METHOD);
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Py_INCREF(self);
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func = PyMethod_GET_FUNCTION(func);
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Py_INCREF(func);
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Py_DECREF(*pfunc);
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*pfunc = self;
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na++;
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n++;
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} else
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Py_INCREF(func);
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READ_TIMESTAMP(*pintr0);
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if (PyFunction_Check(func))
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x = fast_function(func, pp_stack, n, na, nk);
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else
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x = do_call(func, pp_stack, na, nk);
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READ_TIMESTAMP(*pintr1);
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Py_DECREF(func);
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}
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/* Clear the stack of the function object. Also removes
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the arguments in case they weren't consumed already
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(fast_function() and err_args() leave them on the stack).
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*/
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while ((*pp_stack) > pfunc) {
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w = EXT_POP(*pp_stack);
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Py_DECREF(w);
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PCALL(PCALL_POP);
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}
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return x;
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}
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```
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`fast_function` 和 `PyEval_EvalCodeEx` 的代码太长，就不复制粘贴了。源代码（branch: ch11）有一些注释。
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几个和函数参数有关的变量：
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- PyCodeObject->co_argcount
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形参中参数的个数，不包括 *args 和 **kwargs
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- PyCodeObject->co_nlocals
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函数局部变量的个数，包括参数个数（co_argcount + *args + **kwargs）
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- na
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实参中位置参数的个数
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- nw
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实参中关键字参数的个数
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f_localsplus 布局
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```
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PyFrameObject:
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+------------+-------------------+---------------------------+
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| | | |
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| frame_info | extras | valuestack |
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| | | |
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+--------------------------------+---------------------------+
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| |
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<-------------+ f_localsplus +----------------->
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| |
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extras:
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+----------+---------+-------+----------+----------+----------+
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| | | | | | |
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| pos args | kw args | *args | **kwargs | cellvars | freevars |
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| | | | | | |
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+----------+---------+-------+----------+----------+----------+
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```
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cellvars 一般是外层函数使用，存放着被内层嵌套函数引用的变量
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freevars 一般是内层嵌套函数使用，存放着对外层函数中变量的引用
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## 常见的函数定义和调用
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可以使用下面的例子去思考源码中 fast_function和 PyEval_EvalCodeEx的执行流程。
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- 没有参数
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```py
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def f():
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print 'hello world'
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f()
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# co_argcount = 0
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# na = 0, nw = 0
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```
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**符合 fast_function 条件**
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- 只有位置参数
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```py
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def f(a, b):
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print 'hello world'
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f(1, 2)
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# co_argcount = 2
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# na = 2, nw = 0
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f(a=1, b=2)
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# co_argcount = 2
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# na = 0, nw = 2
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```
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**f(1, 2) 符合 fast_function 条件**
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**f(a=1, b=2) 不符合 fast_function 条件**
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- 位置参数和关键字参数
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```py
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def f(a, b, c=1, d=2):
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print 'hello world'
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f(1, 2)
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f(1, 2, 3)
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f(1, 2, 3, 4)
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f(1, 2, c=3)
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f(1, 2, d=3)
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```
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- 可变参数
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```py
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def f(a, b, *args, **kwargs):
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print 'hello world'
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f(1, 2)
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f(1, 2, 3, 4, c=1, d=2)
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```

‎ch12.md‎

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# Python虚拟机中的类机制

‎codes/python_scripts/ch11/func_00.py‎

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def f():
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print 'hello world'
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f()

‎codes/python_scripts/ch11/func_01.py‎

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def f(a, b):
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print a, b
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f(1, 2)

‎codes/python_scripts/ch11/func_02.py‎

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def f(a, b):
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print a, b
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f(1, b=2)

‎codes/python_scripts/ch11/func_03.py‎

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def f(a, b, *args, **kwargs):
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print a, b, args, kwargs
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f(1, 2, 3, 4, c=1, d=2)

‎codes/python_scripts/ch11/func_04.py‎

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def f(a):
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v = 'value'
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def g():
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print v
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return g
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g = f(1)
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g()

‎codes/python_scripts/get_codeobj_info.py‎

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codeobj = compile(src, f_name, 'exec')
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print 'f_consts:', codeobj.co_consts
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print 'code:', codeobj.co_code.encode('hex')
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print 'lnotab:', codeobj.co_lnotab
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def display(codeobj):
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info_keys = [
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'co_filename',
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'co_name',
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'co_firstlineno',
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'co_flags',
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'co_lnotab',
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'co_names',
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'co_argcount',
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'co_nlocals',
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'co_varnames',
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'co_consts',
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'co_cellvars',
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'co_freevars',
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'co_code',
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'co_stacksize',
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]
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print 'code obj info:'
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for k in info_keys:
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v = getattr(codeobj, k)
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print k, ':',
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if k == 'co_code':
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print
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print dis.dis(codeobj)
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elif k == 'co_consts':
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print
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for const in v:
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if hasattr(const, 'co_code'):
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print '----'
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display(const)
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print '----'
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else:
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print const
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else:
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print v
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display(codeobj)
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print dis.dis(codeobj)

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