我在python中学习元编程3.我的教授确实给了我们这个练习：
编写元类法术，在向导中转换学生的实例。
我这样做了：
MainPage.html正确调用向导类var i;
var MAX_ROWS = 5;
var indentations = [0, MAX_ROWS];
var k=Obj.employee.length;
console.log(k);
for(i = k-1; i > 0; i--){
var table = document.getElementById("myTable");
var row = table.insertRow(1);
var cell1 = row.insertCell(0);
var cell2 = row.insertCell(1);
var cell3 = row.insertCell(2);
var cell4 = row.insertCell(3);
var cell5 = row.insertCell(4);
var cell6 = row.insertCell(5);
cell1.innerHTML=Obj.employee[i].email;
cell2.innerHTML=Obj.employee[i].image;
cell3.innerHTML=Obj.employee[i].status;
cell4.innerHTML=Obj.employee[i].mobile;
cell5.innerHTML=Obj.employee[i].college;
cell6.innerHTML='<button class="btn btn-warning" onclick="deleteRow(this)"><span style="color:white"><i class="fa fa-edit"></i> Delete</span></button>';
if (i <= MAX_ROWS) {
var endVal = indentations[indentations.length - 1];
if (i % 5 === 0) { indentations.push(i + MAX_ROWS); }
else if (endVal < k && i == 1) {
endVal = endVal + MAX_ROWS;
indentations.push(endVal);
}
}
}
renderTbl(0, 5);
console.log(indentations);
var before = document.getElementById("myModal");
for (var j = 0, s = indentations.length; j < s; j++) {
var start = indentations[j];
var end = start + MAX_ROWS;
var btn = document.createElement("div");
btn.className = "btn";
btn.innerHTML = start + " ... " + end;
before.insertAdjacentElement("beforeBegin", btn);
}
var btns = document.querySelectorAll(".btn");
for (var j = 0, s = btns.length; j < s; j++) {
var btn = btns[j];
btn.addEventListener("click", function(){
var arr = this.textContent.split("...");
var start = arr[0];
var end = arr[1];
renderTbl(start, end);
});
}
function renderTbl (start, end, arr) {
var table = document.getElementById("myTable");
var rows = table.querySelectorAll("tr");
console.log(rows);
end = parseInt(end);
start = parseInt(start) + 1;
console.log(start) + 1;
console.log(end);
for (var i = 0; i < k; i++) {
console.log(rows[i].innerHTML);
if (i < start || i > end) {
rows[i].style.display = "none";
} else {
rows[i].style.display = "table-row";
}
}
rows[0].style.display = "table-row";
}
而不是学生类class Spell(type):
def __new__(cls, classname, supers, cls_dict):
cls_dict['__init__'] = Spell.toWizard()
cls_dict['__qualname__'] = 'wizard'
return type.__new__(cls, 'wizard', supers, cls_dict)
@staticmethod
def toWizard():
def init(*args):
wizard(args, 'fire_spell')
return init
class student(metaclass=Spell):
def __init__(self, name):
self.name = name
class person():
def __init__(self, name):
self.name = name
class wizard(person):
def __init__(self, name, magic):
self.magic = magic
super().__init__(name)
if __name__ == '__main__':
s = student('name1')
print(s.__dict__)
s = student('name2')
print(s.__dict__)
，但创建的对象为空__init__。我哪里错了？
答案 0 :(得分：7)
您的init()替换函数会创建本地 wizard()实例，并且不会返回任何内容：
def init(*args):
wizard(args, 'fire_spell')
这是一个单独的实例，self未触及。
不要使用__new__;产生一个新类。您只重命名了student类，并为其提供了无效的__init__方法。
重写__call__方法以挂钩创建实例。在那里，您可以替换或忽略第一个参数，即student类对象，并在其位置使用wizard类：
class Spell(type):
def __call__(cls, *args, **kwargs):
# ignore the cls argument, return a wizard instead
if 'magic' not in kwargs and len(args) < 2:
# provide a default magic value
kwargs['magic'] = 'fire_spell'
return wizard(*args, **kwargs)
因为student通常只接受一个参数，所以如果没有指定，则上面添加magic参数。
演示：
>>> student('name1')
<__main__.wizard object at 0x10f1e8198>
>>> vars(_)
{'magic': 'fire_spell', 'name': 'name1'}