[PYTHON] Understanding how to use Jinja2 makes development with Flask smarter
Currently, I am making something like a web service using Flask, but I often get stuck in Jinja2 notation after passing the value from the server side to the client side, so make a note of it.
Overview
- A quick introduction to how to use Flask (if installed, it works with copy and paste)
- There is a Japanese version of Flask's user guide, but the Jinja2 guide is awkward in English.
- Introducing several types of Jinja2 syntax
- Introducing a usage example that combines basic syntax
- You can use Jinja2 to make client-side writing smart.
What is Flask
A micro web development framework for Python. I think there is no problem with Sinatra in Ruby. I think there are many other articles on how to install and use Flask, so I will omit them here. I'm also happy to have a Japanese-language guide like the Flask User Guide. Flask relies on the Jinja2 </ b> template engine and the Werkzeug WSGI toolkit.
The trouble is that there is also a Jinja2 documentation, but this is in English. Jinja2 Documentation
In this article, Flask will describe the basic usage of Jinja2.
First of all, basic Flask usage
Directory structure
First, create a directory such as the project name. Here, qiita_flask is the project name. From the directory structure
qiita_flask
├── app.py
└── templates
└── index.html
Please make it like this. app.py can have a different name, but the templates directory must have this name.
app.py describes server-side processing, and client-side is described in index.html etc. in templates.
Each file
app.py
# coding: utf-8
from flask import Flask, render_template
app = Flask(__name__) #Instance generation
@app.route("/") #When the access route is matched
def hello(): #The hello function works.
return "Hello World!" #On the browser screen"Hello World!"Is output.
@app.route("/index") #application/When the index is accessed
def index():
return render_template('index.html') #/When access comes to index, index in templates.html opens
#This is the point when passing something from the server side to the client side.
if __name__ == "__main__":
#Web server launch
app.run()
index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<script src="http://code.jquery.com/jquery-1.11.1.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-1q8mTJOASx8j1Au+a5WDVnPi2lkFfwwEAa8hDDdjZlpLegxhjVME1fgjWPGmkzs7" crossorigin="anonymous">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js" integrity="sha384-0mSbJDEHialfmuBBQP6A4Qrprq5OVfW37PRR3j5ELqxss1yVqOtnepnHVP9aJ7xS" crossorigin="anonymous"></script>
</head>
<body>
<div class="container">
<div class="header">
<h3 class="text-muted">Sample Page</h3>
</div>
</div>
</body>
</html>
Now let's run app.py. After that, when you access [http: // localhost: 5000](http: // localhost: 5000), you should see "Hello World!" When you visit [http: // localhost: 5000 / index](http: // localhost: 5000 / index), Bootstrap should display Sample Page in a slightly fashionable way. I personally think that it is a good point that you can easily make something like that with Flask + Bootstrap like this. Focusing on the basic usage of Jinja2, there is no further explanation of how to use Flask and Bootstrap.
Basic usage of Jinja2
From this point onward, information will be given from the server side to the client side when calling index.html. To try it out, go to [http: // localhost: 5000 / index](http: // localhost: 5000 / index).
Pass String from server side to client side
app.py
#Omission
@app.route("/index")
def index():
message = 'sample_string'
return render_template('index.html', message=message)
index.html
{#Omission#}
<body>
<div class="container">
<div class="header">
<h3 class="text-muted">Sample Page</h3>
{% if message %}
<p>{{message}}</p>
{% endif %}
</div>
</div>
</body>
Render_template ('index.html', message = message) as above That means passing a variable called message when reading index.html. And on the html side, {% if message%} means that something is in the variable called message. {{message}} will display what is in the variable called message.
Pass a dictionary type variable
app.py
#Omission
@app.route("/index")
def index():
my_dic = {}
my_dic['name'] = ryo2851
my_dic['univ'] = 'hogehoge University'
return render_template('index.html', message=my_dic)
index.html
{#Omission#}
<body>
<div class="container">
<div class="header">
<h3 class="text-muted">Sample Page</h3>
{% if message %}
<p>name: {{message.name}}</p>
<p>univ: {{message.univ}}</p>
{% endif %}
</div>
</div>
</body>
Pass the list
app.py
import numpy as np
#Omission
@app.route("/index")
def index():
num_list = np.arange(10)
return render_template('index.html', message=num_list)
index.html
{#Omission#}
<body>
<div class="container">
<div class="header">
<h3 class="text-muted">Sample Page</h3>
{% for num in message %}
<p>{{num}}</p>
{% endfor %}
</div>
</div>
</body>
A little application
Create a directory for images
Images are saved in a directory called static.
qiita_flask
├── app.py
├── static
│ ├── qiita1.png
│ └── qiita2.png
└── templates
└── index.html
It will be configured like this. Sorry to trouble you, but please prepare a few suitable images. The name is also appropriate and it's okay.
Elements pass a dictionary-type list
For example, if you want to use an image link
<a href = http://hogehoge.com><img src = "hoge.png "> </a>
You need the destination URL and the name of the image, such as. We will send URL and image information from the server side to the client side.
app.py
from os.path import join, relpath
from glob import glob
#Omission
@app.route("/index") #application/When the index is accessed
def index():
path = "./static"
image_names = [relpath(x, path) for x in glob(join(path, '*.png'))]
#In static.png file is image_It is stored in names.
my_list = []
for image in image_names:
my_dic = {}
my_dic['image_name'] = 'static/' + image
my_dic['link_url'] = 'http://qiita.com/ryo2851/items/4e3c287d5a0005780034'
#I couldn't secure many URLs to jump to, so I tried to jump to the same URL for every image.
my_list.append(my_dic)
return render_template('index.html', message = my_list) #/When access comes to index, index in templates.html opens
index.html
{#Omission#}
<body>
<div class="container">
<div class="header">
<h3 class="text-muted">Sample Page</h3>
{% for item in message %}
<a href={{item.link_url}} class="thumbnail"><img src={{item.image_name}}></a>
{% endfor %}
</div>
</body>
The link in the source is my past article. Please have a look if you have time. Now go to / index It should look like this. You can jump to the link by clicking each image.
application
Incorporate Jinja2 in html to be smart.
I want to display the names of members of that grade in a pull-down menu when I press a button like the one in the image below.
Stupid honest coding
Stupid honestly try to write in html
index.html
{#Omission#}
<body>
<div class="container">
<div class="header">
<h3 class="text-muted">Sample Page</h3>
</div>
<hr/>
<div class="btn-group" role="group">
<button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
B4
</button>
<ul class="dropdown-menu">
<li><a href="#">B4taro</a></li>
<li><a href="#">B4Jiro</a></li>
<li><a href="#">B4hanako</a></li>
</ul>
</div>
<div class="btn-group" role="group">
<button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
M1
</button>
<ul class="dropdown-menu">
<li><a href="#">M1taro</a></li>
<li><a href="#">M1Jiro</a></li>
<li><a href="#">M1hanako</a></li>
</ul>
</div>
<div class="btn-group" role="group">
<button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
M2
</button>
<ul class="dropdown-menu">
<li><a href="#">M2taro</a></li>
<li><a href="#">M2Jiro</a></li>
<li><a href="#">M2hanako</a></li>
</ul>
</div>
</div>
</body>
You've written similar code repeatedly.
Coding using Jinja2
I will write using Jinja2 and also on the server side.
app.py
#Omission
@app.route("/index")
def index():
member_dic = {}
B4_list = ['B4taro', 'B4jiro', 'B4hanako']
M1_list = ['M1taro', 'M1jiro', 'M1hanako']
M2_list = ['M2taro', 'M2jiro', 'M2hanako']
member_dic['B4'] = B4_list
member_dic['M1'] = M1_list
member_dic['M2'] = M2_list
return render_template('index.html', message=member_dic)
index.html
{#Omission#}
<body>
<div class="container">
<div class="header">
<h3 class="text-muted">Sample Page</h3>
</div>
<hr/>
{% for grade in message.keys() %}
<div class="btn-group" role="group">
<button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
{{ grade }}
</button>
<ul class="dropdown-menu">
{% for name in message[grade] %}
<li><a href="#">{{ name }}</a></li>
{% endfor %}
</ul>
</div>
{% endfor %}
</div>
</body>
If it is a pattern without ingenuity, for example, when you put in B4, M1, M2, Doctor, Professor, you will want to cry. If you already have a DB with registered members, I think the server side will be simpler. By using Jinja2, I was able to write html on the client side very neatly.
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