Flask学习笔记（基础）

Flask运行原理（源码解读）

https://blog.csdn.net/sinat_36651044/article/details/77532510

1、最简单的开始

|-fflask
    |-static
    |-templates
    |-app.py

 1 from flask import Flask
 2 
 3 app = Flask(__name__)
 4 
 5 
 6 @app.route('/')
 7 def hello_world():
 8     return 'Hello World!'
 9 
10 
11 if __name__ == '__main__':
12     app.run()

app.py

2、Jinja2模板、自定义错误页面、静态文件

 1 from flask import Flask,render_template
 2 
 3 app = Flask(__name__)
 4 
 5 @app.route('/')
 6 def index():
 7     return render_template('index.html')
 8 
 9 @app.route('/user/<name>')
10 def user(name):
11     return render_template('user.html',name=name)
12 
13 @app.route('/hello_world')
14 def hello_world():
15     return 'Hello World!'
16 
17 @app.errorhandler(404)
18 def page_not_found(e):
19     return render_template('404.html'),404
20 
21 @app.errorhandler(500)
22 def errorhandler(e):
23     return render_template('500.html'),500
24 
25 if __name__ == '__main__':
26     app.run()

app.py

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     {% block head %}
 6     <title>----{% block title %}{% endblock %}----</title>
 7     {% endblock %}
 8 </head>
 9 <body>
10 <p>Flask的Base页面</p>
11     {% block body %}
12     {% endblock %}
13 </body>
14 </html>

base.html

1 {% extends 'base.html' %}
2 <!--head在基模板中不是空的，使用super()获取原本内容-->
3 {% block head %}{{ super() }}{% endblock %}
4 {% block title %}首页{% endblock %}
5 {% block body %}首页的body{% endblock %}

index.html

1 {% extends 'base.html' %}
2 {% block head %}{{ super() }}{% endblock %}
3 {% block title %}用户--{{ name }}{% endblock %}
4 {% block body %}{% endblock %}

user.html

1 {% extends 'base.html' %}
2 {% block head %}{{ super() }}{% endblock %}
3 {% block title %}404{% endblock %}
4 {% block body %}
5     <image src="{{ url_for('static',filename='images/404.jpg') }}"></image>
6 {% endblock %}

404.html

1 {% extends 'base.html' %}
2 {% block head %}{{ super() }}{% endblock %}
3 {% block title %}500{% endblock %}
4 {% block body %}<h1>500</h1>{% endblock %}

500.html

3、Web表单 | Flask-WTF

3.1 基础使用，form的创建和验证

 1 from flask import Flask,render_template
 2 from flask_wtf import FlaskForm
 3 from wtforms import StringField,SubmitField
 4 from wtforms.validators import DataRequired,IPAddress
 5 
 6 app = Flask(__name__)
 7 app.config['SECRET_KEY'] = 'key1'
 8 
 9 class NameForm(FlaskForm):
10     name = StringField('你叫啥：',validators=[DataRequired()])
11     ip = StringField('IP地址：',validators=[IPAddress()])
12     submit = SubmitField('提交;-)')
13 
14 
15 @app.route('/',methods=['GET','POST'])
16 def index():
17     name = ''
18     ip = ''
19     form = NameForm()
20     print(name,ip)
21     if form.validate_on_submit():
22         name = form.name.data
23         ip = form.ip.data
24         form.name.data=''
25         form.ip.data=''
26     return render_template('index.html',form=form,name=name,ip=ip)
27 
28 @app.route('/user/<name>')
29 def user(name):
30     return render_template('user.html',name=name)
31 
32 @app.route('/hello_world')
33 def hello_world():
34     return 'Hello World!'
35 
36 @app.errorhandler(404)
37 def page_not_found(e):
38     return render_template('404.html'),404
39 
40 @app.errorhandler(500)
41 def errorhandler(e):
42     return render_template('500.html'),500
43 
44 if __name__ == '__main__':
45     app.run()

app.py

 1 {% extends 'base.html' %}
 2 <!--head在基模板中不是空的，使用super()获取原本内容-->
 3 {% block head %}{{ super() }}{% endblock %}
 4 {% block title %}首页{% endblock %}
 5 {% block body %}
 6     <p>首页的body</p>
 7     <div>
 8     Hello!{{ name }}---{{ ip }}
 9     </div>
10     <div>
11     <form method="post" action="">
12         {{ form.hidden_tag() }}
13         {{ form.name.label }}{{ form.name() }}<br>
14         {{ form.ip.label }}{{ form.ip() }}<br>
15         {{ form.submit() }}
16     </form>
17     </div>
18 {% endblock %}

index.html

3.2 Post/重定向/Get模式，用户会话存储数据

改善用户体验，在post提交后刷新页面不再弹框警告

全局变量session，将数据保存在客户端cookie中

 1 from flask import Flask,render_template,session,redirect,url_for
 2 from flask_wtf import FlaskForm
 3 from wtforms import StringField,SubmitField
 4 from wtforms.validators import DataRequired,IPAddress
 5 
 6 app = Flask(__name__)
 7 app.config['SECRET_KEY'] = 'key1'
 8 
 9 class NameForm(FlaskForm):
10     name = StringField('你叫啥：',validators=[DataRequired()])
11     ip = StringField('IP地址：',validators=[IPAddress()])
12     submit = SubmitField('提交;-)')
13 
14 
15 @app.route('/',methods=['GET','POST'])
16 def index():
17     form = NameForm()
18     if form.validate_on_submit():
19         session['name'] = form.name.data
20         session['ip'] = form.ip.data
21         return redirect(url_for('index'))
22     return render_template('index.html',form=form,name=session.get('name'),ip=session.get('ip'))
23 
24 @app.route('/user/<name>')
25 def user(name):
26     return render_template('user.html',name=name)
27 
28 @app.route('/hello_world')
29 def hello_world():
30     return 'Hello World!'
31 
32 @app.errorhandler(404)
33 def page_not_found(e):
34     return render_template('404.html'),404
35 
36 @app.errorhandler(500)
37 def errorhandler(e):
38     return render_template('500.html'),500
39 
40 if __name__ == '__main__':
41     app.run()

app.py（改动index函数）

3.3 Flash消息

从后端闪现消息给前端

 1 from flask import Flask,render_template,session,redirect,url_for,flash
 2 from flask_wtf import FlaskForm
 3 from wtforms import StringField,SubmitField
 4 from wtforms.validators import DataRequired,IPAddress
 5 
 6 app = Flask(__name__)
 7 app.config['SECRET_KEY'] = 'key1'
 8 
 9 class NameForm(FlaskForm):
10     name = StringField('你叫啥：',validators=[DataRequired()])
11     ip = StringField('IP地址：',validators=[IPAddress()])
12     submit = SubmitField('提交;-)')
13 
14 
15 @app.route('/',methods=['GET','POST'])
16 def index():
17     form = NameForm()
18     if form.validate_on_submit():
19         old_name = session.get('name')
20         if old_name!=None and old_name!=form.name.data:
21             flash('小伙子，看来你改名了！')
22         session['name'] = form.name.data
23         session['ip'] = form.ip.data
24         return redirect(url_for('index'))
25     return render_template('index.html',form=form,name=session.get('name'),ip=session.get('ip'))
26 
27 @app.route('/user/<name>')
28 def user(name):
29     return render_template('user.html',name=name)
30 
31 @app.route('/hello_world')
32 def hello_world():
33     return 'Hello World!'
34 
35 @app.errorhandler(404)
36 def page_not_found(e):
37     return render_template('404.html'),404
38 
39 @app.errorhandler(500)
40 def errorhandler(e):
41     return render_template('500.html'),500
42 
43 if __name__ == '__main__':
44     app.run()

app.py（改动index函数）

 1 {% extends 'base.html' %}
 2 <!--head在基模板中不是空的，使用super()获取原本内容-->
 3 {% block head %}{{ super() }}{% endblock %}
 4 {% block title %}首页{% endblock %}
 5 {% block body %}
 6     <p>首页的body</p>
 7     <div>
 8     Hello!{{ name }}---{{ ip }}
 9     </div>
10     <div>
11     <!--获取后台flash过来的内容-->
12     {% for message in get_flashed_messages() %}
13         {{ message }}
14         {% endfor %}
15     <form method="post" action="">
16         {{ form.hidden_tag() }}
17         {{ form.name.label }}{{ form.name() }}<br>
18         {{ form.ip.label }}{{ form.ip() }}<br>
19         {{ form.submit() }}
20     </form>
21     </div>
22 {% endblock %}

index.html

4、数据库，ORM，Flask-SQLAlchemy

 1 from flask import Flask,render_template,session,redirect,url_for,flash
 2 from flask_wtf import FlaskForm
 3 from wtforms import StringField,SubmitField
 4 from wtforms.validators import DataRequired,IPAddress
 5 from flask_sqlalchemy import SQLAlchemy
 6 
 7 app = Flask(__name__)
 8 app.config['SECRET_KEY'] = 'key1'
 9 app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+pymysql://root:root@127.0.0.1/world?charset=utf8'
10 app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True
11 app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
12 db = SQLAlchemy(app)
13 
14 class NameForm(FlaskForm):
15     name = StringField('你叫啥：',validators=[DataRequired()])
16     ip = StringField('IP地址：',validators=[IPAddress()])
17     submit = SubmitField('提交;-)')
18 
19 class Role(db.Model):
20     __tablename__ = 'roles'
21     id = db.Column(db.Integer,primary_key=True)
22     name = db.Column(db.String(64),unique=True)
23     users = db.relationship('User',backref='role')
24     def __repr__(self):
25         return '<Role %r>'%self.name
26 
27 class User(db.Model):
28     __tablename__ = 'users'
29     id = db.Column(db.Integer,primary_key=True)
30     username = db.Column(db.String(64),unique=True,index=True)
31     role_id = db.Column(db.Integer,db.ForeignKey('roles.id'))
32     def __repr__(self):
33         return '<Role %r>'%self.username
34 
35 
36 
37 
38 @app.route('/',methods=['GET','POST'])
39 def index():
40     form = NameForm()
41     if form.validate_on_submit():
42         user = User.query.filter_by(username=form.name.data).first()
43         if user is None:
44             user = User(username=form.name.data)
45             db.session.add(user)
46             session['known'] = False
47         else:
48             session['known'] = True
49         session['name'] = form.name.data
50         form.name.data=''
51         return redirect(url_for('index'))
52     return render_template('index.html',form=form,name=session.get('name'),ip=session.get('ip'))
53 
54 @app.route('/user/<name>')
55 def user(name):
56     return render_template('user.html',name=name)
57 
58 @app.route('/hello_world')
59 def hello_world():
60     return 'Hello World!'
61 
62 @app.errorhandler(404)
63 def page_not_found(e):
64     return render_template('404.html'),404
65 
66 @app.errorhandler(500)
67 def errorhandler(e):
68     return render_template('500.html'),500
69 
70 if __name__ == '__main__':
71     app.run()

app.py

 1 {% extends 'base.html' %}
 2 <!--head在基模板中不是空的，使用super()获取原本内容-->
 3 {% block head %}{{ super() }}{% endblock %}
 4 {% block title %}首页{% endblock %}
 5 {% block body %}
 6     <p>首页的body</p>
 7     <div>
 8     Hello!{{ name }}---{{ ip }}
 9     </div>
10     <div>
11     <h1>hello,{% if name %}{{ name }}{% else %}陌生人{% endif %}</h1>
12     {% if not know %}
13         <p>很高兴认识你</p>
14     {% else %}
15         <p>很高兴再见到你</p>
16     {% endif %}
17     <form method="post" action="">
18         {{ form.hidden_tag() }}
19         {{ form.name.label }}{{ form.name() }}<br>
20         {{ form.ip.label }}{{ form.ip() }}<br>
21         {{ form.submit() }}
22     </form>
23     </div>
24 {% endblock %}

index.html

 1 #配置数据库连接
 2 app = Flask(__name__)
 3 app.config['SECRET_KEY'] = 'key1'
 4 app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+pymysql://root:root@127.0.0.1/world?charset=utf8'
 5 app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True
 6 app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
 7 db = SQLAlchemy(app)
 8 
 9 #定义模型
10 class NameForm(FlaskForm):
11     name = StringField('你叫啥：',validators=[DataRequired()])
12     ip = StringField('IP地址：',validators=[IPAddress()])
13     submit = SubmitField('提交;-)')
14 
15 class Role(db.Model):
16     __tablename__ = 'roles'
17     id = db.Column(db.Integer,primary_key=True)
18     name = db.Column(db.String(64),unique=True)
19     users = db.relationship('User',backref='role')
20     def __repr__(self):
21         return '<Role %r>'%self.name
22 
23 #创建删除表，可以在flask shell中操作
24 db.create_all()
25 db.drop_all()
26 
27 #增
28 admin_role = Role(name='Admin')
29 user1 = User(username='Jim',role=admin_role)
30 db.session.add(admin_role)
31 db.session.add(user1)
32 db.session.commit()
33 
34 #查
35 #查全部，返回列表
36 Role.query.all() 
37 #查单个，返回query对象
38 admin_role = Role.query.filter_by(name='Admin').first()
39 
40 #删
41 db.session.delete(admin_role)
42 db.session.commit()
43 
44 #改
45 admin_role.name = 'AD'
46 db.session.add(admin_role)
47 db.session.commit()
48 
49 #回滚，在commit前都可以回滚到上次commit时的状态
50 db.seesion.rollback()

建增删改查

查看sql语句

str(Role.query.filter_by(name='Admin').first())