Python locals() 的陷阱
// bltinmodule.cstatic PyMethodDef builtin_methods[] = {... // 找到 locals 函数对应的内置函数是 builtin_locals
{"locals", (PyCFunction)builtin_locals, METH_NOARGS, locals_doc},
...
}
-----------------------------// builtin_locals 的定义static PyObject *
builtin_locals(PyObject *self)
{
PyObject *d;
d = PyEval_GetLocals();
Py_XINCREF(d); return d;
}
-----------------------------
PyObject *
PyEval_GetLocals(void)
{
PyFrameObject *current_frame = PyEval_GetFrame();// 获取当前堆栈对象
if (current_frame == NULL) return NULL;
PyFrame_FastToLocals(current_frame); // 初始化和填充 f_locals
return current_frame->f_locals;
}
-----------------------------// 初始化和填充 f_locals 的具体实现void
PyFrame_FastToLocals(PyFrameObject *f)
{ /* Merge fast locals into f->f_locals */
PyObject *locals, *map;
PyObject **fast;
PyObject *error_type, *error_value, *error_traceback;
PyCodeObject *co;
Py_ssize_t j; int ncells, nfreevars; if (f == NULL) return;
locals = f->f_locals;
// 如果locals为空, 就新建一个字典对象
if (locals == NULL) {
locals = f->f_locals = PyDict_New();
if (locals == NULL) {
PyErr_Clear(); /* Can't report it :-( */
return;
}
}
co = f->f_code;
map = co->co_varnames; if (!PyTuple_Check(map)) return;
PyErr_Fetch(&error_type, &error_value, &error_traceback);
fast = f->f_localsplus;
j = PyTuple_GET_SIZE(map); if (j > co->co_nlocals)
j = co->co_nlocals;
// 将 f_localsplus 写入 locals
if (co->co_nlocals)
map_to_dict(map, j, locals, fast, 0);
ncells = PyTuple_GET_SIZE(co->co_cellvars);
nfreevars = PyTuple_GET_SIZE(co->co_freevars); if (ncells || nfreevars) { // 将 co_cellvars 写入 locals
map_to_dict(co->co_cellvars, ncells,
locals, fast + co->co_nlocals, 1);
if (co->co_flags & CO_OPTIMIZED) { // 将 co_freevars 写入 locals
map_to_dict(co->co_freevars, nfreevars,
locals, fast + co->co_nlocals + ncells, 1);
}
}
PyErr_Restore(error_type, error_value, error_traceback);
}
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