当前位置：网站首页>[flask tutorial] flask development foundation and introduction

[flask tutorial] flask development foundation and introduction

2022-06-25 12:57:00 【Coconut brine Engineer】

One 、Flask Medium Hello World

from flask import Flask
app = Flask(__name__) 

@app.route('/') // route 
def hello_world():
    return 'Hello World!'

if __name__ == '__main__':
    app.run()

Two 、Flask Routing and reverse routing

1） Custom routing

Import required request

Add route ：

@app.route('/user')
def hello():
    return 'Hello user'

Check out the browser ：
Insert picture description here
Appoint HTTP Method ：

@app.route('/login', methods=['GET', 'POST'])
def hello():
    return 'Hello user'

Transfer of parameters on route ：

@app.route('/user/<id>')
def show_post(post_id):
    return 'Post %d' % post_id

@app.route('/user/query_user')
def hello_getid():
    id=request.args.get('id')
    return 'Hello user!'+id

Insert picture description here

2） Reverse routing

Backward derivation of route through view function .

Import required url_for

@app.route('/user/query_user')
def hello_getid():
    id=request.args.get('id')
    return 'Hello user!'+id

@app.route('/query_url')
def query_url():
    return 'query url:'+url_for('hello_getid')

Insert picture description here

3、 ... and 、Flask Template

use Python Generate HTML Very boring , And it's pretty cumbersome , Because you have to do it manually HTML Do turn Meaning to ensure the security of the application . So ,Flask Equipped with a Jinja2 template engine .

You can use render_template() Method to render the template . One thing you need to do Cutting is to pass the template name and the parameters you want as keywords into the variables of the template .

1） Basic example

mian.py

from flask import Flask,render_template
app = Flask(__name__)

@app.route('/')
def hello_world():
    return render_template("index.html")

if __name__ == '__main__':
    app.run()

Flask Will be in templates Looking for templates in the folder . therefore , If your application is a module , this A folder should be at the same level as the module ; If it's a bag , So this folder is a subdirectory of the package :

/templates/index.html

<!doctype html>
<title>Hello from Flask</title>
{
    % if name %}
  <h1>Hello {
    {
     name }}!</h1>
{
    % else %}
  <h1>Hello World hhh!</h1>
{
    % endif %}

The directory structure is as follows ：
Insert picture description here

2） Transfer the required data to the template

app.py

@app.route('/')
def hello_world():
    content = " Pass you something "
    return render_template("index.html",content=content)

/templates/index.html

<!doctype html>
<title>Hello from Flask</title>
{
    % if name %}
  <h1>Hello {
    {
     name }}!</h1>
{
    % else %}
  <h1>{
    {
    content}}</h1>
{
    % endif %}

Insert picture description here

3） Pass more complex data to the template ：user class

models.py

class User(object):
    def __init__(self,user_id,user_name):
        self.user_id=user_id
        self.user_name=user_name

templates/user_index.html

<!doctype html>
<title>Hello from Flask</title>
{
    % if name %}
  <h1>hello {
    {
     user.user_name }}!</h1>
{
    % else %}
  <h1>hello {
    {
    user.user_id}}</h1>
{
    % endif %}

main.py

from flask import Flask,request,url_for,render_template
from models import User
app = Flask(__name__)

@app.route('/')
def hello_world():
    content = " Pass you something "
    return render_template("index.html", content=content)

@app.route('/user')
def user_index():
   user = User(1,'hhhh')
   return render_template("user_index.html",user=user)
   
if __name__ == '__main__':
    app.run()

It is shown in the figure below ：
Insert picture description here

4） Conditional template rendering

main.py

@app.route('/query_user/<user_id>')
def query_user(user_id):
   user = None
   if int(user_id)==1:
       user =User(1,'hhhhh')
   return render_template("user_id.html",user=user)

user_id.html

<!doctype html>
<title>Hello from Flask</title>
{
    % if user %}
  <h1>hello {
    {
     user.user_name }}!</h1>
{
    % else %}
  <h1>no this user</h1>
{
    % endif %}

It is shown in the figure below ：
Insert picture description here

Four 、Flask Message prompt and exception reminder

Flask Provide message flash mechanism in , You can simply give feedback to users . The message flashing system usually records information at the end of the request , And in the next （ And only in the next ） request Access recorded information in . The presentation of these messages is usually combined with a template layout .

Use flash() Method can flash a message . To manipulate the message itself , Please use get_flashed_messages() function , And it can also be used in templates .

1） Message tip

main.py

from flask import Flask,request,url_for,render_template, flash
app = Flask(__name__)
app.secret_key = '123'

@app.route('/')
def hello_world():
    flash("hello")
    return render_template("index.html")
if __name__ == '__main__':
    app.run()

index.html

<!doctype html>
<title>Hello from Flask</title>
  <h1>Hello !</h1>
  <h2>{
    {
    get_flashed_messages()[0]}}</h2>

2） for instance ： Login message prompt

index.html

<!doctype html>
<title>Hello from Flask</title>
  <h1>Hello !</h1>
    <form action="/login" method="post">
      <input type="text" name="username">
      <input type="password" name="password">
      <input type="submit" value="Submit">
    </form>
  <h2>{
    {
    get_flashed_messages()[0]}}</h2>

mian.py

def login():
    form = request.form
    username = form.get('username')
    password = form.get('password')

    if not username:
        flash(' Please enter a user name ')
        return render_template("index.html")
    if not password:
        flash(' Please input a password ')
        return render_template('index.html')
    if username == 'admin' and password== 'admin':
        flash(' Landing successful ')
        return render_template('index.html')
    else:
        flash(' Wrong user name or password ')
        return render_template('index.html')

The operation results are as follows ：
Insert picture description here

3） exception handling

mian.py

@app.errorhandler(404)
def not_found(e):
    return render_template('404.html')

404.html

<!doctype html>
<html>
<head>
  <meta charset="UTF-8">
  <title>404</title>
</head>
<body>
<h1> The page you're looking for doesn't exist </h1>
</body>
</html>