start Flask and create a simple project Supporting tagline
Part One : install flask and make it work on laptop.
step 1.install falsk on mac
sudo easy_install virtualenv
or
sudo pip install virtualenv
virtualenv can separate different python projects from its Environment.
step 2.cerate environment：
mkdir myproject
cd myproject
virtualenv env
then it would come the information below.
“New python executable in env/bin/python”
“Installing setuptools…………done.”
step 3.active its environment:
. env/bin/activate
take care about the dot and the space ,if this command can not be used , try to use source
step 4.active Flask in your virtualenv:
easy_install Flask
Part Two : Start Flask project.
step 5.write a file named “hello.py”,with code below :
from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello_world():
return "Hello World!"
if __name__ == '__main__':
app.run()
Then run python hello.py,we can see “Hello World!” in http://127.0.0.1:5000/
how it works?
import Flask tell us to create a WSGI program.
then route tell us which page will trigger this function hello_world()
we use app.run() to run the local server , Ctrl+C to stop.
if we want to interview this project from outside, use app.run(host='0.0.0.0')
Some details:
details 1 : add app.debug = True,it will let us to debug the project from server . but please remember,
we can not use app.debug = True under Production, cause this allow user to run his code in Production.
details 2 : we can use variable to set the RUL
@app.route('/user/<username>')
def show_user_profile(username):
return username
@app.route('/post/<int:post_id>')
def show_post(post_id):
return post_id
we can use int,float,path to limit the type of input.
details 3 : HTTP methods
in route(), we can add methods= ['get','post']
@app.route('/login', methods=['GET', 'POST'])
def login():
if request.method == 'POST':
do_the_login()
else:
show_the_login_form()
details 4 : static files
create a folder /static , js or CSS can be stored here,if style.css under this folder,use url_for('static', filename='style.css') to interview this file.
details 5 : template
Flask use Jinja2 as render_templates, use render_template() to render templates,put the pages under templates.
from flask import render_template
@app.route('/hello/')
@app.route('/hello/<name>')
def hello(name=None):
return render_template('hello.html', name=name)
then Flask will find “hello.html” under templates
details 6 : files upload
remember set enctype="multipart/form-data" in the html form.
it will create a request object with its attribute file,and use save() to save.
and please never believe its “file_name” ,this name will be faked easily. so use secure_filename() to make it safe .
from flask import request
from werkzeug import secure_filename
@app.route('/upload', methods=['GET', 'POST'])
def upload_file():
if request.method == 'POST':
f = request.files['the_file']
f.save('/var/www/uploads/' + secure_filename(f.filename))
... ...
details 7 : redirect and ERROR
if we want to jump to another URL, use redirect(); if we want to interrupt a request and return flase info, use abort()
from flask import abort, redirect, url_for
@app.route('/')
def index():
return redirect(url_for('login'))
@app.route('/login')
def login():
abort(401)
this_is_never_executed()
details 8 : log
there is a class Logger,use like this :
app.logger.debug('A value for debugging')
app.logger.warning('A warning occurred (%d apples)', 42)
app.logger.error('An error occurred')
Part Three : create a project by flask
the project is here
then we start it step by step.
one : create folders for this project
create /static and /templates under /flaskr. “static” is for user request, also we put CSS and JS here;”templates” for rendering templates, all the templates will be put here.
two : deploy
in order to create db information, create “schema.sql”, Click here.
three : create a main module
create a file named “flaskr.py”, and add
# all the imports
import sqlite3
from flask import Flask, request, session, g, redirect, url_for, \ abort, render_template, flash
# configuration
DATABASE = '/tmp/flaskr.db'
DEBUG = True
SECRET_KEY = 'development key'
USERNAME = 'admin'
PASSWORD = 'default'
username is “admin” and password is “default”.
then create app, in the same py file
# create our application
app = Flask(__name__)
app.config.from_object(__name__)
of course , we need to link to the db, so also add
def connect_db():
return sqlite3.connect(app.config['DATABASE'])
at last , start server with
if __name__ == '__main__':
app.run()
four : create db for app and link
create db by
sqlite3 /tmp/flaskr.db < schema.sql
then link by
@app.before_request
def before_request():
g.db = connect_db()
@app.after_request
def after_request(response):
g.db.close()
return response
“@app.before_request” can be called before rquest, and “@app.after_request” can be call after request.
five : view functions
we need functions to show the views. here’s the functions we want.
“show_entries()” for ”/”, to show index.
“add_entry()” for “/add”, to add new archives.
“login()” for “/login”, for user to login in .
“logout()” for “/logout”, for user to logout.
so all the code is here.
six : add templates.
templates inculdes “layout.html”,”show_entries.html”,”login.html”
please check here.
seven : add CSS
add “style.css” under “static” , check here .
eight : start server
at last, start server with “python flaskr.py”.
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