UnboundLocalError：在 Django 中赋值之前引用的局部变量 'form'

Question

所以我正在从事一个Django项目，这是我的views.py文件：

def new_topic(request, pk):
    board = get_object_or_404(Board, pk=pk)
    user = User.objects.first()  # TODO: get the currently logged in user
    if request.method == 'POST':
        form = NewTopicForm(request.POST)
    if form.is_valid():
        topic = form.save()
        return redirect('board_topics', pk=board.pk)
    else:
        form = NewTopicForm()
    return render(request, 'new_topic.html', {'form': form})

当我运行服务器时，我有一个错误说：

UnboundLocalError: local variable 'form' referenced before assignment

这是我的new_topic.html文件

{% extends 'base.html' %}
{% block title %}Start a New Topic{% endblock %}
{% block breadcrumb %}
    <li class="breadcrumb-item"><a href="{% url 'home' %}">Boards</a></li>
    <li class="breadcrumb-item"><a href="{% url 'board_topics' board.pk %}">{{ board.name }}</a></li>
    <li class="breadcrumb-item active">New topic</li>
{% endblock %}
{% block content %}
    <form method="post">
        {% csrf_token %}
        {{ form.as_p }}
        <button type="submit" class="btn btn-success">Post</button>
    </form>
{% endblock %}

Answer 1

if form.is_valid():在 GET请求上失败，因为您仅定义 form时request.method == 'POST'。

可以通过更改一些凹痕来解决：

if request.method == 'POST':
    form = NewTopicForm(request.POST)
    if form.is_valid():
        topic = form.save()
        return redirect('board_topics', pk=board.pk)
else:
    form = NewTopicForm()
return render(request, 'new_topic.html', {'form': form})

Answer 2

我没有发现缩进的任何问题，而是初始化。在渲染之前请初始化！进行更改如下所示，肯定会奏效，这是一种消除它的非常真实且正确的方法：

def new_topic(request, pk):
    board = get_object_or_404(Board, pk=pk)
    user = User.objects.first()  # TODO: get the currently logged in user
    form = NewTopicForm()
    if request.method == 'POST':
        form = NewTopicForm(request.POST)
        if form.is_valid():
           topic = form.save()
           return redirect('board_topics', pk=board.pk)
        else:
            form = NewTopicForm()
    return render(request, 'new_topic.html', {'form': form})