tf.keras.losses.SparseCategoricalCrossentropy() 稀疏交叉熵损失函数示例

# 编写你的第一个 Django 应用，第 3 部分¶
这一篇从教程第 2 部分结尾的地方继续讲起。我们将继续编写投票应用，并且专注于如何创建公用界面——也被称为“视图”。

概况¶

Django 中的视图的概念是「一类具有相同功能和模板的网页的集合」。比如，在一个博客应用中，你可能会创建如下几个视图：

/newsarchive///

编写更多视图

polls/views.py

def detail(request, question_id):
    return HttpResponse("You're looking at question %s." % question_id)
def results(request, question_id):
    response = "You're looking at the results of question %s."
    return HttpResponse(response % question_id)
def vote(request, question_id):
    return HttpResponse("You're voting on question %s." % question_id)

polls.urlsurl()

from django.urls import path
from . import views
urlpatterns = [
    # ex: /polls/
    path('', views.index, name='index'),
    # ex: /polls/5/
    path('<int:question_id>/', views.detail, name='detail'),
    # ex: /polls/5/results/
    path('<int:question_id>/results/', views.results, name='results'),
    # ex: /polls/5/vote/
    path('<int:question_id>/vote/', views.vote, name='vote'),
]

detail()mysite.urlsROOT_URLCONFurlpatterns'polls/'"polls/""34/"'/'detail()

detail(request=<HttpRequest object>, question_id=34)

question_id=34:question_id>int:.html

path('polls/latest.html', views.index),

但是，别这样做，这太傻了。

写一个真正有用的视图

HttpResponseHttp404HttpResponseindex()

from django.http import HttpResponse
from .models import Question
def index(request):
    latest_question_list = Question.objects.order_by('-pub_date')[:5]
    output = ', '.join([q.question_text for q in latest_question_list])
    return HttpResponse(output)
# Leave the rest of the views (detail, results, vote) unchanged

pollstemplatesTEMPLATESDjangoTemplatesAPP_DIRSDjangoTemplatesINSTALLED_APPStemplatespollsindex.htmlpolls/templates/polls/index.htmlapp_directoriespolls/index.htmlpolls/templatespolls

{% if latest_question_list %}
    <ul>
    {% for question in latest_question_list %}
        <li><a href="/polls/{{ question.id }}/">{{ question.question_text }}</a></li>
    {% endfor %}
    </ul>
{% else %}
    <p>No polls are available.</p>
{% endif %}

polls/views.pyindex

from django.http import HttpResponse
from django.template import loader
from .models import Question
def index(request):
    latest_question_list = Question.objects.order_by('-pub_date')[:5]
    template = loader.get_template('polls/index.html')
    context = {
        'latest_question_list': latest_question_list,
    }
    return HttpResponse(template.render(context, request))

polls/index.html

render()

HttpResponseindex()

from django.shortcuts import render
from .models import Question
def index(request):
    latest_question_list = Question.objects.order_by('-pub_date')[:5]
    context = {'latest_question_list': latest_question_list}
    return render(request, 'polls/index.html', context)

loaderHttpResponsedetailresultsvoteHttpResponserender()HttpResponse

抛出 404 错误

现在，我们来处理投票详情视图——它会显示指定投票的问题标题。下面是这个视图的代码：
polls/views.py

from django.http import Http404
from django.shortcuts import render
from .models import Question
# ...
def detail(request, question_id):
    try:
        question = Question.objects.get(pk=question_id)
    except Question.DoesNotExist:
        raise Http404("Question does not exist")
    return render(request, 'polls/detail.html', {'question': question})

Http404polls/detail.html

{{ question }}

这样你就能测试了。

get_object_or_404()

get()Http404detail()

from django.shortcuts import get_object_or_404, render
from .models import Question
# ...
def detail(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return render(request, 'polls/detail.html', {'question': question})

get()Http404get_object_or_404()ObjectDoesNotExistObjectDoesNotExistHttp404django.shortcutsget_list_or_404()get_object_or_404()get()filter()Http404

使用模板系统

detail()questionpolls/detail.html

<h1>{{ question.question_text }}</h1>
<ul>
{% for choice in question.choice_set.all %}
    <li>{{ choice.choice_text }}</li>
{% endfor %}
</ul>

{{ question.question_text}}question{% for %}question.choice_set.allquestion.choice_set.all()Choice{% for %}

去除模板中的硬编码 URL

polls/index.html

<li><a href="/polls/{{ question.id }}/">{{ question.question_text }}</a></li>

polls.urlsurl(){% url %}

<li><a href="{% url 'detail' question.id %}">{{ question.question_text }}</a></li>

polls.urls

...
# the 'name' value as called by the {% url %} template tag
path('<int:question_id>/', views.detail, name='detail'),
...

polls/specifics/12/polls/urls.py

...
# added the word 'specifics'
path('specifics/<int:question_id>/', views.detail, name='detail'),
...

为 URL 名称添加命名空间¶

pollspollsdetail{% url %}polls/urls.pyapp_name

from django.urls import path
from . import views
app_name = 'polls'
urlpatterns = [
    path('', views.index, name='index'),
    path('<int:question_id>/', views.detail, name='detail'),
    path('<int:question_id>/results/', views.results, name='results'),
    path('<int:question_id>/vote/', views.vote, name='vote'),
]

polls/index.html

<li><a href="{% url 'detail' question.id %}">{{ question.question_text }}</a></li>

修改为指向具有命名空间的详细视图：
polls/templates/polls/index.html

<li><a href="{% url 'polls:detail' question.id %}">{{ question.question_text }}</a></li>

当你对你写的视图感到满意后，请阅读教程的第 4 部分了解简单的表单处理和通用视图。

tf.keras.losses.SparseCategoricalCrossentropy() 稀疏交叉熵 损失函数 示例

概况¶