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Building Web Applications with Flask
Building Web Applications with Flask

Building Web Applications with Flask: Use Python and Flask to build amazing web applications, just the way you want them!

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Profile Icon Italo Maia Profile Icon Italo M Campelo Maia Profile Icon Gareth Dwyer Profile Icon Jack Stouffer
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€18.99 per month
Full star icon Full star icon Full star icon Full star icon Empty star icon 4 (1 Ratings)
Paperback Jun 2015 160 pages 1st Edition
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€15.99 €23.99
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€29.99
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Arrow left icon
Profile Icon Italo Maia Profile Icon Italo M Campelo Maia Profile Icon Gareth Dwyer Profile Icon Jack Stouffer
Arrow right icon
€18.99 per month
Full star icon Full star icon Full star icon Full star icon Empty star icon 4 (1 Ratings)
Paperback Jun 2015 160 pages 1st Edition
eBook
€15.99 €23.99
Paperback
€29.99
Subscription
Free Trial
Renews at €18.99p/m
eBook
€15.99 €23.99
Paperback
€29.99
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Free Trial
Renews at €18.99p/m

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Building Web Applications with Flask

Chapter 2. First App, How Hard Could it Be?

After a full chapter without a single line of code, you need this, right? In this chapter, we will write our first app explained line by line; we will also cover how to set up our environment, what tools to use for development, and how to work with HTML in our app.

Hello World

The first app one writes when learning a new technology is usually a Hello World app, which consists of the minimum possible code necessary to start a simple application and show the text "Hello World!". Let's do exactly that using Flask.

This book is optimized for Python 2.x, so, that's the version I advise you to use from now on. All the examples and code are aimed at that Python version, which is the default in most Linux distributions.

Prerequisites and tools

First, let's make sure our environment is properly configured. For this course, I assume you are using a Debian-like Linux distribution, such as Mint (http://www.linuxmint.com/) or Ubuntu (http://ubuntu.com/). All the instructions will be geared towards these systems.

Let's begin by installing the required Debian packages with apt-get as follows:

sudo apt-get install python-dev python-pip

This will install the Python development tools and libraries required for compiling Python packages, and pip: a neat tool you can use to install Python packages from the command line. On with it! Let's install our virtual environment managing tool:

sudo pip install virtualenvwrapper
echo "source /usr/local/bin/virtualenvwrapper.sh" >> ~/.bashrc

To explain what we just did: sudo tells our OS that we want administrative privileges to run the next command, and pip is the default Python package management tool and helps us install the virtualenvwrapper package...

Setting up a virtual environment

A virtual environment is the way Python isolates full package environments from one another. This means you can easily manage dependencies. Imagine you want to define the minimum necessary packages for a project; a virtual environment would be perfect to let you test and export the list of needed packages. We will discuss it later on. Now, create a new terminal pressing Ctrl + Shift + T on your keyboard and create our hello world environment like this:

mkvirtualenv hello
pip install flask

The first line creates our environment with the name "hello". You will also automatically load that environment into the current terminal. You can deactivate your virtual environment by typing deactivate and you can load it again with the following command:

workon hello  # substitute hello with the desired environment name if needed

The second line tells pip to install the Flask package in the current virtual environment, hello in this case.

Understanding the "Hello World" app

Given the environment set, what should we use to write our beautiful code? An editor or an IDE? If you're working on a low budget, try Light Table editor (http://lighttable.com/). Free, fast, and easy to use (Ctrl + Spacebar gives you access to all available options), it also has workspace support! Can't get any better for the money. If you're a lucky one with $200 to spare (or if you have a free license https://www.jetbrains.com/pycharm/buy/), just fork out for the PyCharm IDE which is pretty much the best IDE for Python Web development. Now let's move on.

Create a folder that will hold your project files (you don't need to but people will like you more if you do), as follows:

mkdir hello_world

Enter the new project folder and create the main.py file:

cd hello_world
touch main.py

The main.py file will have the whole "Hello World" application in it. Our main.py content should be like this:

# coding:utf-8
from flask...

Serving HTML pages

First, to make our hello function respond with HTML, all we have to do is change it like this:

def hello():
    return "<html><head><title>Hi there!</title></head><body>Hello World!</body></html>", 200

In the preceding example, hello is returning a HTML formatted string and a number. The string will be parsed as HTML by default while 200 is an optional HTTP code indicating a successful response. 200 is returned by default.

If you refresh your browser with F5, you'll notice that nothing has changed. That's why the Flask development server is not reloading when the source changes. That only happens when you run your application in debug mode. So let's do that:

app = Flask(__name__)
app.debug=True

Now go to the terminal where your application is running, type Ctrl + C then restart the server. You will notice a new output besides the URL where your server is running—something about "stat&quot...

Hello World


The first app one writes when learning a new technology is usually a Hello World app, which consists of the minimum possible code necessary to start a simple application and show the text "Hello World!". Let's do exactly that using Flask.

This book is optimized for Python 2.x, so, that's the version I advise you to use from now on. All the examples and code are aimed at that Python version, which is the default in most Linux distributions.

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Description

If you are a Python web developer who wants to learn more about developing applications in Flask and scaling them with industry-standard practices, this is the book for you.

Who is this book for?

If you are a Python web developer who wants to learn more about developing applications in Flask and scaling them with industry-standard practices, this is the book for you.

What you will learn

  • Create single page applications with Flask
  • Use macros, filters, tags, and control structures to render rich responses to user requests
  • Receive forms securely through formbased classes and WTForms
  • Utilize NoSQL or SQL databases to store user data seamlessly
  • Generate simple, yet powerful, REST services from your data models
  • Learn how to perform testdriven and behaviordriven developments in your Flask projects
  • Use Flask components to create maintainable nonflat projects
  • Harvest the power of extensions to build robust authorization and permission policies

Product Details

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Publication date : Jun 26, 2015
Length: 160 pages
Edition : 1st
Language : English
ISBN-13 : 9781784396152
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Length: 160 pages
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Language : English
ISBN-13 : 9781784396152
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Tools :

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Table of Contents

11 Chapters
1. Flask in a Flask, I Mean, Book Chevron down icon Chevron up icon
2. First App, How Hard Could it Be? Chevron down icon Chevron up icon
3. Man, Do I Like Templates! Chevron down icon Chevron up icon
4. Please Fill in This Form, Madam Chevron down icon Chevron up icon
5. Where Do You Store Your Stuff? Chevron down icon Chevron up icon
6. But I Wanna REST Mom, Now! Chevron down icon Chevron up icon
7. If Ain't Tested, It Ain't Game, Bro! Chevron down icon Chevron up icon
8. Tips and Tricks or Flask Wizardry 101 Chevron down icon Chevron up icon
9. Extensions, How I Love Thee Chevron down icon Chevron up icon
10. What Now? Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

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Po-An, Yang Oct 10, 2015
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
It can be batter with python 3.
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