Django入门指南：从基础到实践

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"这是一份详细的Django学习文档，适合初学者，涵盖了Django的各个方面，包括模型、视图、模板、表单、开发过程、管理界面、安全、国际化、性能优化、Python兼容性等核心内容，并提供了入门教程，逐步指导如何创建第一个Django应用。" Django是基于Python的Web框架，它强调代码的简洁性和可读性，旨在提高开发效率。这份深入浅出的Django学习文档是了解和掌握这个框架的理想资源，特别适合Python开发者作为基础学习材料。 1. **获取帮助** - 文档中包含了各种获取Django支持和社区资源的方法，对于初学者来说，这是解决遇到问题时的重要参考。 2. **入门步骤** - 阐述了如何开始Django项目，包括安装、环境配置等基础操作。 3. **模型层** - Django的核心之一，用于定义数据库结构，处理数据操作。在这里，你可以学习到如何定义模型类，以及它们与数据库的关系。 4. **视图层** - 视图负责处理HTTP请求并返回响应。这部分将解释如何编写视图函数，如何处理不同的请求类型。 5. **模板层** - 模板是HTML文件，用于呈现数据。文档会介绍Django模板语言，包括变量插入、控制结构和过滤器等。 6. **表单** - Django提供了一种方便的方式来处理用户输入，创建表单和验证数据。这部分会教你如何定义和使用表单。 7. **开发过程** - 文档中可能涵盖版本控制、调试技巧、测试策略等内容，帮助开发者建立良好的开发习惯。 8. **管理界面（Admin）** - Django的内置管理界面可以快速创建后台管理功能，方便管理网站内容。 9. **安全** - 讲解如何确保Django应用的安全，如防止SQL注入、跨站脚本攻击等。 10. **国际化与本地化** - Django支持多语言应用，这部分会教你怎么实现应用的全球化。 11. **性能与优化** - 提供了提高Django应用性能的建议，如缓存、数据库查询优化等。 12. **Python兼容性** - Django通常会支持多个Python版本，文档会指出兼容的范围。 13. **地理框架** - Django提供了地理数据的支持，适用于需要处理地理位置信息的应用。 14. **常见Web应用工具** - 可能包括中间件、URL路由、静态文件处理等内容。 15. **其他核心功能** - 这部分可能包含Django框架的其他特色功能和组件。 16. **Django开源项目** - 介绍了Django的社区和贡献机制，鼓励读者参与到开源项目中。文档还提供了从快速安装到编写完整应用的详细教程，分为多个部分，覆盖了创建应用的全过程，包括数据库设计、视图、模板、表单的使用，以及应用部署等。此外，还有关于如何为Django贡献代码的指南，适合想要参与开源项目的开发者。无论你是完全新手还是有一定经验的开发者，这份文档都能为你提供宝贵的知识和实践指导。

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2.1.5 Design your URLs

A clean, elegant URL scheme is an important detail in a high-quality Web application. Django encourages beautiful

URL design and doesn’t put any cruft in URLs, like .php or .asp.

To design URLs for an app, you create a Python module called a URLconf . A table of contents for your app, it contains

a simple mapping between URL patterns and Python callback functions. URLconfs also serve to decouple URLs from

Python code.

Here’s what a URLconf might look like for the Reporter/Article example above:

from django.conf.urls import url

urlpatterns = [

url(r’^articles/(\d{4})/$’, ’news.views.year_archive’),

url(r’^articles/(\d{4})/(\d{2})/$’, ’news.views.month_archive’),

url(r’^articles/(\d{4})/(\d{2})/(\d+)/$’, ’news.views.article_detail’),

]

The code above maps URLs, as simple regular expressions, to the location of Python callback functions (“views”).

The regular expressions use parenthesis to “capture” values from the URLs. When a user requests a page, Django runs

through each pattern, in order, and stops at the ﬁrst one that matches the requested URL. (If none of them matches,

Django calls a special-case 404 view.) This is blazingly fast, because the regular expressions are compiled at load

time.

Once one of the regexes matches, Django imports and calls the given view, which is a simple Python function. Each

view gets passed a request object – which contains request metadata – and the values captured in the regex.

For example, if a user requested the URL “/articles/2005/05/39323/”, Django would call the function

news.views.article_detail(request, ’2005’, ’05’, ’39323’).

2.1.6 Write your views

Each view is responsible for doing one of two things: Returning an HttpResponse object containing the content

for the requested page, or raising an exception such as Http404. The rest is up to you.

Generally, a view retrieves data according to the parameters, loads a template and renders the template with the

retrieved data. Here’s an example view for year_archive from above:

from django.shortcuts import render

def year_archive(request, year):

a_list = Article.objects.filter(pub_date__year=year)

context = {’year’: year, ’article_list’: a_list}

return render(request, ’news/year_archive.html’, context)

This example uses Django’s template system, which has several powerful features but strives to stay simple enough

for non-programmers to use.

2.1.7 Design your templates

The code above loads the news/year_archive.html template.

Django has a template search path, which allows you to minimize redundancy among templates. In your Django

settings, you specify a list of directories to check for templates with TEMPLATE_DIRS. If a template doesn’t exist in

the ﬁrst directory, it checks the second, and so on.

Let’s say the news/year_archive.html template was found. Here’s what that might look like:

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{% extends "base.html" %}

{% block title %}Articles for {{ year }}{% endblock %}

{% block content %}

<h1>Articles for {{ year }}</h1>

{% for article in article_list %}

<p>{{ article.headline }}</p>

<p>By {{ article.reporter.full_name }}</p>

<p>Published {{ article.pub_date|date:"F j, Y" }}</p>

{% endfor %}

{% endblock %}

Variables are surrounded by double-curly braces. {{ article.headline }} means “Output the value of the

article’s headline attribute.” But dots aren’t used only for attribute lookup. They also can do dictionary-key lookup,

index lookup and function calls.

Note {{ article.pub_date|date:"F j, Y" }} uses a Unix-style “pipe” (the “|” character). This is called

a template ﬁlter, and it’s a way to ﬁlter the value of a variable. In this case, the date ﬁlter formats a Python datetime

object in the given format (as found in PHP’s date function).

You can chain together as many ﬁlters as you’d like. You can write custom template ﬁlters. You can write custom

template tags, which run custom Python code behind the scenes.

Finally, Django uses the concept of “template inheritance”. That’s what the {% extends "base.html" %}

does. It means “First load the template called ‘base’, which has deﬁned a bunch of blocks, and ﬁll the blocks with

the following blocks.” In short, that lets you dramatically cut down on redundancy in templates: each template has to

deﬁne only what’s unique to that template.

Here’s what the “base.html” template, including the use of static ﬁles, might look like:

{% load staticfiles %}

<html>

<head>

<title>{% block title %}{% endblock %}</title>

</head>

<body>

{% block content %}{% endblock %}

</body>

</html>

Simplistically, it deﬁnes the look-and-feel of the site (with the site’s logo), and provides “holes” for child templates to

ﬁll. This makes a site redesign as easy as changing a single ﬁle – the base template.

It also lets you create multiple versions of a site, with different base templates, while reusing child templates. Django’s

creators have used this technique to create strikingly different mobile versions of sites – simply by creating a new base

template.

Note that you don’t have to use Django’s template system if you prefer another system. While Django’s template

system is particularly well-integrated with Django’s model layer, nothing forces you to use it. For that matter, you

don’t have to use Django’s database API, either. You can use another database abstraction layer, you can read XML

ﬁles, you can read ﬁles off disk, or anything you want. Each piece of Django – models, views, templates – is decoupled

from the next.

2.1. Django at a glance 11

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2.1.8 This is just the surface

This has been only a quick overview of Django’s functionality. Some more useful features:

• A caching framework that integrates with memcached or other backends.

• A syndication framework that makes creating RSS and Atom feeds as easy as writing a small Python class.

• More sexy automatically-generated admin features – this overview barely scratched the surface.

The next obvious steps are for you to download Django, read the tutorial and join the community. Thanks for your

interest!

2.2 Quick install guide

Before you can use Django, you’ll need to get it installed. We have a complete installation guide that covers all

the possibilities; this guide will guide you to a simple, minimal installation that’ll work while you walk through the

introduction.

2.2.1 Install Python

Being a Python Web framework, Django requires Python. It works with Python 2.7, 3.2, 3.3, or 3.4. All these versions

of Python include a lightweight database called SQLite so you won’t need to set up a database just yet.

Get the latest version of Python at http://www.python.org/download/ or with your operating system’s package manager.

Django on Jython

If you use Jython (a Python implementation for the Java platform), you’ll need to follow a few additional steps. See

Running Django on Jython for details.

You can verify that Python is installed by typing python from your shell; you should see something like:

Python 3.3.3 (default, Nov 26 2013, 13:33:18)

[GCC 4.8.2] on linux

Type "help", "copyright", "credits" or "license" for more information.

>>>

2.2.2 Set up a database

This step is only necessary if you’d like to work with a “large” database engine like PostgreSQL, MySQL, or Oracle.

To install such a database, consult the database installation information.

2.2.3 Remove any old versions of Django

If you are upgrading your installation of Django from a previous version, you will need to uninstall the old Django

version before installing the new version.

2.2.4 Install Django

You’ve got three easy options to install Django:

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• Install a version of Django provided by your operating system distribution. This is the quickest option for those

who have operating systems that distribute Django.

• Install an ofﬁcial release. This is the best approach for users who want a stable version number and aren’t

concerned about running a slightly older version of Django.

• Install the latest development version. This is best for users who want the latest-and-greatest features and aren’t

afraid of running brand-new code.

Always refer to the documentation that corresponds to the version of Django you’re using!

If you do either of the ﬁrst two steps, keep an eye out for parts of the documentation marked new in development

version. That phrase ﬂags features that are only available in development versions of Django, and they likely won’t

work with an ofﬁcial release.

2.2.5 Verifying

To verify that Django can be seen by Python, type python from your shell. Then at the Python prompt, try to import

Django:

>>> import django

>>> print(django.get_version())

1.8

You may have another version of Django installed.

2.2.6 That’s it!

That’s it – you can now move onto the tutorial.

2.3 Writing your ﬁrst Django app, part 1

Let’s learn by example.

Throughout this tutorial, we’ll walk you through the creation of a basic poll application.

It’ll consist of two parts:

• A public site that lets people view polls and vote in them.

• An admin site that lets you add, change and delete polls.

We’ll assume you have Django installed already. You can tell Django is installed and which version by running the

following command:

$ python -c "import django; print(django.get_version())"

If Django is installed, you should see the version of your installation. If it isn’t, you’ll get an error telling “No module

named django”.

This tutorial is written for Django 1.8 and Python 3.2 or later. If the Django version doesn’t match, you can refer to

the tutorial for your version of Django by using the version switcher at the bottom right corner of this page, or update

Django to the newest version. If you are still using Python 2.7, you will need to adjust the code samples slightly, as

described in comments.

See How to install Django for advice on how to remove older versions of Django and install a newer one.

2.3. Writing your ﬁrst Django app, part 1 13

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Where to get help:

If you’re having trouble going through this tutorial, please post a message to django-users or drop by #django on

irc.freenode.net to chat with other Django users who might be able to help.

2.3.1 Creating a project

If this is your ﬁrst time using Django, you’ll have to take care of some initial setup. Namely, you’ll need to auto-

generate some code that establishes a Django project – a collection of settings for an instance of Django, including

database conﬁguration, Django-speciﬁc options and application-speciﬁc settings.

From the command line, cd into a directory where you’d like to store your code, then run the following command:

$ django-admin.py startproject mysite

This will create a mysite directory in your current directory. If it didn’t work, see Problems running django-

admin.py.

Note: You’ll need to avoid naming projects after built-in Python or Django components. In particular, this means

you should avoid using names like django (which will conﬂict with Django itself) or test (which conﬂicts with a

built-in Python package).

Where should this code live?

If your background is in plain old PHP (with no use of modern frameworks), you’re probably used to putting code

under the Web server’s document root (in a place such as /var/www). With Django, you don’t do that. It’s not a

good idea to put any of this Python code within your Web server’s document root, because it risks the possibility that

people may be able to view your code over the Web. That’s not good for security.

Put your code in some directory outside of the document root, such as /home/mycode.

Let’s look at what startproject created:

mysite/

manage.py

mysite/

__init__.py

settings.py

urls.py

wsgi.py

Doesn’t match what you see?

The default project layout recently changed. If you’re seeing a “ﬂat” layout (with no inner mysite/ directory),

you’re probably using a version of Django that doesn’t match this tutorial version. You’ll want to either switch to the

older tutorial or the newer Django version.

These ﬁles are:

• The outer mysite/ root directory is just a container for your project. Its name doesn’t matter to Django; you

can rename it to anything you like.

• manage.py: A command-line utility that lets you interact with this Django project in various ways. You can

read all the details about manage.py in django-admin.py and manage.py.

14 Chapter 2. Getting started

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