Python中的kwargs参数的可变性 [英] Mutability of the **kwargs argument in Python
本文介绍了Python中的kwargs参数的可变性的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
kwargs
dict: def print_arg(** kwargs):
打印kwargs.pop('key')
如果我用这样的字典调用方法 pop_arg
:
mydict = {'key':'value'}
print_arg(** mydict)
将<?c $ c> mydict 由此电话更改?
我也对基础的更详细的解释感兴趣方法调用机制让 mydict
更改。
解决方案
:
import dis
dis.dis(lambda:print_arg(** {'key':'value' ))
6 0 LOAD_GLOBAL 0(print_arg)
3 BUILD_MAP 1
6 LOAD_CONST 1('value')
9 LOAD_CONST 2('key')
12 STORE_MAP
13 CALL_FUNCTION_KW 0
16 RETURN_VALUE
我们来看看什么 CALL_FUNCTION_KW
( ceval .c
):
case CALL_FUNCTION_VAR:
case CALL_FUNCTION_KW:
case CALL_FUNCTION_VAR_KW:
{
// ...
x = ext_do_call(func,& sp,flags,na,nk);
// ...
static PyObject *
ext_do_call(PyObject * func,PyObject *** pp_stack,int flags,int na,int nk)
{
int nstar = 0;
PyObject * callargs = NULL;
PyObject * stararg = NULL;
PyObject * kwdict = NULL;
PyObject * result = NULL;
if(flags& CALL_FLAG_KW){//如果**涉及
kwdict = EXT_POP(* pp_stack); //获取带有**
的dict传递if(!PyDict_Check(kwdict)){
PyObject * d;
d = PyDict_New(); // make a new dict
if(d == NULL)
goto ext_call_fail;
if(PyDict_Update(d,kwdict)!= 0){//用旧的
//更新它// .. .. ..
goto ext_call_fail;
}
Py_DECREF(kwdict);
kwdict = d; // kwdict现在是新的dict
}
}
....
result = PyObject_Call(func,callargs,kwdict); // call with new dict
Consider a case where I change the kwargs
dict inside a method:
def print_arg(**kwargs):
print kwargs.pop('key')
If I call the method pop_arg
with a dictionary like this:
mydict = {'key':'value'}
print_arg(**mydict)
will mydict
be changed by this call?
I am also interested in a more detailed explanation of the underlying method calling mechanism that lets mydict
change or not.
解决方案
Let's see:
import dis
dis.dis(lambda: print_arg(**{'key': 'value'}))
6 0 LOAD_GLOBAL 0 (print_arg)
3 BUILD_MAP 1
6 LOAD_CONST 1 ('value')
9 LOAD_CONST 2 ('key')
12 STORE_MAP
13 CALL_FUNCTION_KW 0
16 RETURN_VALUE
Let's find what CALL_FUNCTION_KW
does (ceval.c
):
case CALL_FUNCTION_VAR:
case CALL_FUNCTION_KW:
case CALL_FUNCTION_VAR_KW:
{
// ...
x = ext_do_call(func, &sp, flags, na, nk);
// ...
static PyObject *
ext_do_call(PyObject *func, PyObject ***pp_stack, int flags, int na, int nk)
{
int nstar = 0;
PyObject *callargs = NULL;
PyObject *stararg = NULL;
PyObject *kwdict = NULL;
PyObject *result = NULL;
if (flags & CALL_FLAG_KW) { // if ** is involved
kwdict = EXT_POP(*pp_stack); // get the dict passed with **
if (!PyDict_Check(kwdict)) {
PyObject *d;
d = PyDict_New(); // make a NEW dict
if (d == NULL)
goto ext_call_fail;
if (PyDict_Update(d, kwdict) != 0) { // update it with old
// .. fail ..
goto ext_call_fail;
}
Py_DECREF(kwdict);
kwdict = d; // kwdict is now the new dict
}
}
....
result = PyObject_Call(func, callargs, kwdict); // call with new dict
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