Flask Web Development: Developing Web Applications with Python

by Miguel Grinberg

Overview

Take full creative control of your web applications with Flask, the Python-based microframework. With the second edition of this hands-on book, you’ll learn Flask from the ground up by developing a complete, real-world application created by author Miguel Grinberg. This refreshed edition accounts for important technology changes that have occurred in the past three years.

Explore the framework’s core functionality, and learn how to extend applications with advanced web techniques such as database migrations and an application programming interface. The first part of each chapter provides you with reference and background for the topic in question, while the second part guides you through a hands-on implementation.

If you have Python experience, you’re ready to take advantage of the creative freedom Flask provides. Three sections include:

• A thorough introduction to Flask: explore web application development basics with Flask and an application structure appropriate for medium and large applications
• Building Flasky: learn how to build an open source blogging application step-by-step by reusing templates, paginating item lists, and working with rich text
• Going the last mile: dive into unit testing strategies, performance analysis techniques, and deployment options for your Flask application

Product Details

ISBN-13:	9781491991732
Publisher:	O'Reilly Media, Incorporated
Publication date:	03/30/2018
Edition description:	2nd ed.
Pages:	312
Product dimensions:	7.00(w) x 9.10(h) x 0.70(d)

About the Author

Miguel Grinberg has over 25 years of experience as a software engineer. He blogs at https://blog.miguelgrinberg.com about a variety of topics including web development, Python, robotics, photography and the occasional movie review. Miguel lives in Portland, Oregon.

Table of Contents

Preface xi

Part I Introduction to Flask

1 Installation 1

Creating the Application Directory 2

Virtual Environments 2

Creating a Virtual Environment with Python 3 3

Creating a Virtual Environment with Python 2 3

Working with a Virtual Environment 4

Installing Python Packages with pip 5

2 Basic Application Structure 7

Initialization 7

Routes and View Functions 8

A Complete Application 9

Development Web Server 10

Dynamic Routes 12

Debug Mode 13

Command-Line Options 15

The Request-Response Cycle 17

Application and Request Contexts 17

Request Dispatching 18

The Request Object 19

Request Hooks 20

Responses 21

Flask Extensions 23

3 Templates 25

The Jinja2 Template Engine 26

Rendering Templates 26

Variables 27

Control Structures 28

Bootstrap Integration with Flask-Bootstrap 30

Custom Error Pages 33

Links 36

Static Files 37

Localization of Dates and Times with Flask-Moment 38

4 Web Forms 43

Configuration 44

Form Classes 44

HTML Rendering of Forms 47

Form Handling in View Functions 48

Redirects and User Sessions 51

Message Flashing 53

5 Databases 57

SQL Databases 57

No SQL Databases 58

SQL or NoSQL? 59

Python Database Frameworks 59

Database Management with Flask-SQLAlchemy 61

Model Definition 62

Relationships 64

Database Operations 66

Creating the Tables 66

Inserting Rows 66

Modifying Rows 68

Deleting Rows 68

Querying Rows 68

Database Use in View Functions 71

Integration with the Python Shell 72

Database Migrations with Flask-Migrate 73

Creating a Migration Repository 73

Creating a Migration Script 74

Upgrading the Database 75

Adding More Migrations 76

6 Email 79

Email Support with Flask-Mail 79

Sending Email from the Python Shell 81

Integrating Emails with the Application 81

Sending Asynchronous Email 83

7 Large Application Structure 85

Project Structure 85

Configuration Options 86

Application Package 88

Using an Application Factory 88

Implementing Application Functionality in a Blueprint 90

Application Script 93

Requirements File 93

Unit Tests 94

Database Setup 96

Running the Application 97

Part II Example: A Social Slogging Application

8 User Authentication 101

Authentication Extensions for Flask 101

Password Security 102

Hashing Passwords with Werkzeug 102

Creating an Authentication Blueprint 105

User Authentication with Flask-Login 107

Preparing the User Model for Logins 107

Protecting Routes 108

Adding a Login Form 109

Signing Users In 111

Signing Users Out 112

Understanding How Flask-Login Works 113

Testing Logins 114

New User Registration 115

Adding a User Registration Form 115

Registering New Users 117

Account Confirmation 118

Generating Confirmation Tokens with itsdangerous 118

Sending Confirmation Emails 120

Account Management 125

9 User Roles 127

Database Representation of Roles 127

Role Assignment 131

Role Verification 132

10 User Profiles 137

Profile Information 137

User Profile Page 138

Profile Editor 141

User-Level Profile Editor 141

Administrator-Level Profile Editor 143

User Avatars 146

11 Blog Posts 151

Blog Post Submission and Display 151

Blog Posts on Profile Pages 154

Paginating Long Blog Post Lists 155

Creating Fake Blog Post Data 155

Rendering in Pages 157

Adding a Pagination Widget 158

Rich-Text Posts with Markdown and Flask-PageDown 161

Using Flask-PageDown 162

Handling Rich Text on the Server 164

Permanent Links to Blog Posts 165

Blog Post Editor 167

12 Followers 171

Database Relationships Revisited 171

Many-to-Many Relationships 172

Self-Referential Relationships 174

Advanced Many-to-Many Relationships 174

Followers on the Profile Page 178

Querying Followed Posts Using a Database Join 181

Showing Followed Posts on the Home Page 183

13 User Comments 189

Database Representation of Comments 189

Comment Submission and Display 191

Comment Moderation 193

14 Application Programming Interfaces 199

Introduction to REST 199

Resources Are Everything 200

Request Methods 201

Request and Response Bodies 201

Versioning 202

RESTful Web Services with Flask 203

Creating an API Blueprint 203

Error Handling 204

User Authentication with Flask-HTTPAuth 206

Token-Based Authentication 208

Serializing Resources to and from JSON 210

Implementing Resource Endpoints 213

Pagination of Large Resource Collections 216

Testing Web Services with HTTPie 217

Part III The Last Mile

15 Testing 221

Obtaining Code Coverage Reports 221

The Flask Test Client 224

Testing Web Applications 225

Testing Web Services 228

End-to-End Testing with Selenium 230

Is It Worth It? 234

16 Performance 237

Logging Slow Database Performance 237

Source Code Profiling 239

17 Deployment 241

Deployment Workflow 241

Logging of Errors During Production 242

Cloud Deployment 243

The Heroku Platform 244

Preparing the Application 244

Testing with Heroku Local 253

Deploying with git push 254

Deploying an Upgrade 255

Docker Containers 256

Installing Docker 256

Building a Container Image 257

Running a Container 261

Inspecting a Running Container 262

Pushing Your Container Image to an External Registry 263

Using an External Database 264

Container Orchestration with Docker Compose 265

Cleaning Up Old Containers and Images 269

Using Docker in Production 270

Traditional Deployments 270

Server Setup 271

Importing Environment Variables 271

Setting Up Logging 272

18 Additional Resources 275

Using an Integrated Development" Environment (IDE) 275

Finding Flask Extensions 276

Getting Help 276

Getting Involved with Flask 277

Index 279