利用Python Flask构建Web网站

jieforest · 发表于 2012-10-16 13:01

File organization and management script

In our example, our application is a single file. As you can guess, this will not suffice as it becomes larger.
I find a good approach is to treat the app as a python module. The module name will be the app name and the initialization of the Flask object is done in the __init__.py file.

The templates/ folder will be located inside the module’s directory as well as any other files related to our application (eg. settings.py, models.py…).

example/
__init__.py
static/
favicon.ico
templates/
index.html
hello.html

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jieforest · 发表于 2012-10-16 13:02

Note: as the application grows larger, you should use Flask’s Blueprints to organize your code as modules. I will cover that in another tutorial.

I also like to use the Flask-Script extension to manage my application from the command line. This extension provides built-in commands as well as a mechanism to define your own ones.

$ pip install Flask-Assets

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jieforest · 发表于 2012-10-16 13:02

I configure and run the extension from a manage.py file located outside the module’s directory:

#!/usr/bin/env python
from flaskext.script import Manager, Shell, Server
from example import app
manager = Manager(app)
manager.add_command("runserver", Server())
manager.add_command("shell", Shell())
manager.run()

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jieforest · 发表于 2012-10-16 13:02

To start the server from the command line:

$ ./manage.py runserver

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jieforest · 发表于 2012-10-16 13:03

Using a database

There is no out of the box support for any database with Flask. Which is not a problem as there are many database libraries in Python. The most known and the one I prefer is SqlAlchemy. In addition to its excellent database toolkit, it features an awesome ORM.

Integrating SqlAlchemy with Flask cannot be simpler, thanks to the Flask-SqlAlchemy extension.

$ pip install Flask-SqlAlchemy

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jieforest · 发表于 2012-10-18 12:13

本帖最后由 jieforest 于 2012-10-18 12:14 编辑

If it’s your first time with SqlAlchemy, I would advice reading the ORM tutorial which is a very good start.

I like to initialize the extension and configure my models in a models.py file.

from flask_sqlalchemy import SQLAlchemy
from example import app
db = SQLAlchemy(app)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String)
message = db.Column(db.String)
def __init__(self, username, message):
self.username = username
self.message = message

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jieforest · 发表于 2012-10-18 12:14

We’ll then need to add the database connection parameters to the configuration. For this example, we’ll usesqlite. In __init__.py add this line after the previous app.config one:

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite://example.db'

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jieforest · 发表于 2012-10-18 12:15

We can now modify our example to use the model, in __init__.py:

from models import *
# ...
@app.route('/signup', methods=['POST'])
def signup():
user = User(request.form['username'], request.form['message'])
db.session.add(user)
db.session.commit()
return redirect(url_for('message', username=user.username))
@app.route('/message/<username>')
def message(username):
user = User.query.filter_by(username=username).first_or_404()
return render_template('message.html', username=user.username,
message=user.message)

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jieforest · 发表于 2012-10-18 12:16

Instead of using the session we are now creating a User object, storing it into the database usingdb.session.add() and db.session.commit() (which is the standard SqlAlchemy way of doing it).

In the message() function I have added a username parameter which must be given through the url’s path. We next perform a database query using User.query. Note the first_or_404() function which is provided by the flask extension and is a nice addition.

jieforest · 发表于 2012-10-18 12:20

Configuration

As we’ve seen in the previous example, the configuration can be defined using the app.config dict. While this is the easier method, it is not the most practical one once you factor in configuration environments. Indeed, the configuration of your app will most of the time be different between your development environment and your production one.

The Flask documentation suggests a nice way of handling these configuration environments.

We’ll store our configuration as attributes of plain old python objects in a file called settings.py. After reading the current environment form a system environment variable (EXAMPLE_ENV in our case) we’ll load the config from the correct config object.

In the settings.py file as follow:

class Config(object):
SECRET_KEY = 'secret key'
class ProdConfig(Config):
SQLALCHEMY_DATABASE_URI = 'postgresql://localhost/example'
class DevConfig(Config):
DEBUG = True
SQLALCHEMY_DATABASE_URI = 'sqlite://example.db'
SQLALCHEMY_ECHO = True

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