Python列表值被覆盖，为什么? [英] Python list value gets overwritten, why?

问题描述

我有一个收件人查询，其中包含两个具有 ID 1和2 的收件人:我遍历每一个以构建json输出:

I have a recipients query containing two recipients with the ID 1 and 2: I loop over each one to build json output:

    data = []
    this_tem = {}

    for item in recipients:
        this_tem['recipient_id'] = item.pk
        data.append(this_tem)

    return HttpResponse(json.dumps(data), mimetype='application/json')

这给了我

[
    {
        "recipient_id": 2,
    },
    {
        "recipient_id": 2,
    }
]

如您所见，它应该是 recipient_id 1 和 recipient_id 2 ，但是，我的循环会覆盖该值，为什么?

As you can see it should be recipient_id 1 and recipient_id 2 however, my loop overwrites the value, why?

推荐答案

this_tem 是对单个对象(字典)的引用，您可以对其进行反复修改并附加到循环中.您将在循环中覆盖该键的值.

this_tem is a reference to a single object (a dict) which you repeatedly modify and append in your loop. You overwrite the value of that key in the loop.

您需要在每次迭代中创建一个新的字典:

You need to create a new dict each iteration:

data = []

for item in recipients:
    this_tem = {}
    this_tem['recipient_id'] = item.pk
    data.append(this_tem)

修改
正如Grijesh Chauhan亲切指出的那样，相对于列表理解，可以简化表达式和循环:

Edit
As Grijesh Chauhan graciously pointed out, the expression and loop can be simplified vis a vie a list comprehension:

data = [{'recipient_id': item.pk} for item in recipients]

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