如何在不创建列表的情况下添加到 python 中的列表答案

【问题标题】：How can i add to a list in python without creating it如何在不创建列表的情况下添加到 python 中的列表
【发布时间】：2020-11-02 13:58:56
【问题描述】：

我有以下 django 视图来查找问卷的平均分数。

@login_required
def statistics(request, slug=False):
    qn = get_object_or_404(Questionnaire, slug=slug)
    questions = Question.objects.filter(questionnaire=qn).count()
    qs = Question.objects.filter(questionnaire=qn)
    responses = Response.objects.filter(question__in=qs, user=request.user).count()
    if questions == 0 or responses == 0 or not questions <= responses:
        return render(request, "questionnaire/stats.html")
    out = {}
    for q in qs:
        response = Response.objects.filter(question=q, user=request.user).order_by("session_datetime").first()
        out[q.category] = {}
        time = response.session_datetime
        time_string = time.strftime("%d/%m/%Y")
        out[q.category][time_string] = []
        responses_in_time = Response.objects.filter(question=q, user=request.user, session_datetime__gte=time,
                                                    session_datetime__lt=time + datetime.timedelta(hours=24))
        for res in responses_in_time:
            out[q.category][time_string] += [res.value]
    print(out)
    for category in out.keys():
        print("outcat"+ str(out[category]))
        for time in out[category].keys():
            out[category][time] = sum(out[category][time])/len(out[category][time])
    print(out)
    return render(request, "questionnaire/stats.html", context={"questionnaire": qn, "stats_json": json.dumps(out)})

我想知道是否有一种方法可以将字典与循环中的模型/记录中的时间放在一起而无需每次都重置它，如果我尝试 += 而不先创建它会抱怨但我不知道循环内的初始时间。

【问题讨论】：

标签： python python-3.x django list loops

【解决方案1】：

好的，所以我不知道为什么我只能在我发布后才想出答案，但这是工作代码。通过循环两次，一次创建字典，一次填充它，我已经解决了这个问题。

@login_required
def statistics(request, slug=False):
    qn = get_object_or_404(Questionnaire, slug=slug)
    questions = Question.objects.filter(questionnaire=qn).count()
    qs = Question.objects.filter(questionnaire=qn)
    responses = Response.objects.filter(question__in=qs, user=request.user).count()
    if questions == 0 or responses == 0 or not questions <= responses:
        return render(request, "questionnaire/stats.html")
    out = {}
    response = Response.objects.filter(question=qs.first(), user=request.user).order_by("session_datetime").first()
    time = response.session_datetime
    time_string = time.strftime("%d/%m/%Y")
    for q in qs:
        out[q.category] = {}
        out[q.category][time_string] = []
    for q in qs:
        responses_in_time = Response.objects.filter(question=q, user=request.user, session_datetime__gte=time,
                                                    session_datetime__lt=time + datetime.timedelta(hours=24))
        for res in responses_in_time:
            out[q.category][time_string] += [res.value]
    print(out)
    for category in out.keys():
        print("outcat"+ str(out[category]))
        for time in out[category].keys():
            out[category][time] = sum(out[category][time])/len(out[category][time])
    print(out)
    return render(request, "questionnaire/stats.html", context={"questionnaire": qn, "stats_json": json.dumps(out)})

【讨论】：