1、URL
1.1、how url works
1.1.1、recive a httprequest
1.1.2、find urls.py in the root URLconf
1.1.3、test the requested URL against each url entry.（every app can have a urls.py,but we always start with the root urls.py）
1.2、def url(regex, view, kwargs=None, name=None):
1.3、url匹配處理是從上到下的，匹配後就會返回view，注意先後順序
1.3.1 If you want to design cool URLs for user profiles, the easiest solution to avoid URL collision is by adding a prefix like /u/vitorfs/, or like Medium does /@vitorfs/, where “@” is the prefix.
2、regex（正則表達式）
https://simpleisbetterthancomplex.com/references/2016/10/10/url-patterns.html
3、attribute PK
pk stands for Primary Key. It’s a shortcut for accessing a model’s primary key. All Django models have this attribute.
For the most cases, using the pk property is the same as id. That’s because if we don’t define a primary key for a model, Django will automatically create an AutoField named id, which will be its primary key.
If you defined a different primary key for a model, for example, let’s say the field email is your primary key. To access it you could either use obj.email or obj.pk.
4、testcase
5、Reusable Templates
5.1、create a base.html（模板） under templates/
5.2、leave{%block name%}{%endblock%} to be extends by other html
5.3、use home.html and topics.html to extends base.html,use {%block name%} {%endblock%} to fill in certain block
!use
{% extends 'base.html' %}to claim the html you extend
example:
base.html
{% load static %}<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>{% block title %}Django Boards{% endblock %}</title>
<link rel="stylesheet" href="{% static 'css/bootstrap.min.css' %}">
</head>
<body>
<div class="container">
<ol class="breadcrumb my-4">
{% block breadcrumb %}
{% endblock %}
</ol>
{% block content %}
{% endblock %}
</div>
</body>
</html>home.html
{% extends 'base.html' %}
{% block breadcrumb %}
<li class="breadcrumb-item active">Boards</li>
{% endblock %}