Python plays well with others

 

Python can integrate with COM,.NET, and CORBA objects.

 

For Java libraries, use Jython, an implementation of Python for the Java Virtual Machine.

 

For.NET, try IronPython, Microsoft's new implementation of Python for.NET, or Python for.NET.

 

Python is also supported for the Internet Communications Engine (ICE) and many other integration technologies.

 

If you find something that Python cannot do, or if you need the performance advantage of low-level code, you can write extension modules in C or C++, or wrap existing code with SWIG or Boost.Python. Wrapped modules appear to your program exactly like native Python code. That's language integration made easy. You can also go the opposite route and embed Python in your own application, providing your users with a language they'll enjoy using.

 

Python runs everywhere

 

Python is available for all major operating systems: Windows, Linux/Unix, OS/2, Mac, Amiga, among others. There are even versions that run on.NET and the Java virtual machine. You'll be pleased to know that the same source code will run unchanged across all implementations.

 

Your favorite system isn't listed here? It may still support Python if there's a C compiler for it. Ask around on news: comp.lang.python - or just try compiling

Python yourself.

 

Python is friendly... and easy to learn

 

The Python newsgroup is known as one of the friendliest around. The avid developer and user community maintains a wiki, hosts international and local conferences, runs development sprints, and contributes to online code repositories.

 

Python also comes with complete documentation, both integrated into the language and as separate web pages. Online tutorials target both the seasoned programmer and the newcomer. All are designed to make you productive quickly. The availability of first-rate books completes the learning package.

 

Python is Open

 

The Python implementation is under an open source license that makes it freely usable and distributable, even for commercial use. The Python license is administered by the Python Software Foundation.

 

 

3.2 Django

A web application framework is a software framework that is designed to support the development of dynamic websites, web applications and web services.

 

The framework aims to alleviate the overhead associated with common activities performed in Web development.

 

Basically, a web framework makes it easier for you to develop your application. Most sites have a common set of functionality (like handling sessions, data validation, etc) and a framework is something that prevents you from re-writing this each time you create a website.

 

LAMP (Linux, Apache, MySQL, PHP/Perl/Python) is a package that contains a web server (Apache). This is a piece of software that actually runs your web application. Frameworks are, in short, libraries that help you develop faster. Flask is a micro framework, which basically means that it is a framework with a small footprint (and meant for small sites, according to its docs). Django & Ruby on Rails are also frameworks. Django and Flask are both frameworks for Python, but Rails is a framework for Ruby.

 

Most developers suggest that we build applications without the help of frameworks, and then jump into using frameworks (which require us to understand principles such as Model-View-Controller, ORM, and so forth).

 

Because I’ve learned a lot of basic principles of building applications I’ve chosen the python-based web framework names Django.

 

In the early days, Web developers wrote every page by hand. Updating a Web site meant editing HTML; a “redesign” involved redoing every single page, one at a time.

 

As Web sites grew and became more ambitious, it quickly became obvious that that situation was tedious, time-consuming, and ultimately untenable. A group of enterprising hackers at NCSA (the National Center for Supercomputing Applications, where Mosaic, the first graphical Web browser, was developed) solved this problem by letting the Web server spawn external programs that could dynamically generate HTML. They called this protocol the Common Gateway Interface, or CGI, and it changed the Web forever. It’s hard now to imagine what a revelation CGI must have been: instead of treating HTML pages as simple files on disk, CGI allows you to think of your pages as resources generated dynamically on demand. The development of CGI ushered in the first generation of dynamic Web sites.

 

However, CGI has its problems: CGI scripts need to contain a lot of repetitive “boilerplate” code, they make code reuse difficult, and they can be difficult for first-time developers to write and understand.

 

PHP fixed many of these problems, and it took the world by storm – it’s now by far the most popular tool used to create dynamic Web sites, and dozens of similar languages and environments (ASP, JSP, etc.) followed PHP‟s design closely. PHP‟s major innovation is its ease of use: PHP code is simply embedded into plain HTML; the learning curve for someone who already knows HTML is extremely shallow.

 

But PHP has its own problems; its very ease of use encourages sloppy, repetitive, ill-conceived code. Worse, PHP does little to protect programmers from security vulnerabilities, and thus many PHP developers found themselves learning about security only once it was too late.

 

These and similar frustrations led directly to the development of the current crop of “third-generation” Web development frameworks. These frameworks – Django and Ruby on Rails appear to be the most popular these days – recognize that the Web’s importance has escalated of late. With this new explosion of Web development comes yet another increase in ambition; Web developers are expected to do more and more every day.

 

Django was invented to meet these new ambitions. Django lets you build deep, dynamic, interesting sites in an extremely short time. Django is designed to let you focus on the fun, interesting parts of your job while easing the pain of the repetitive bits. In doing so, it provides high-level abstractions of common Web development patterns, shortcuts for frequent programming tasks, and clear conventions on how to solve problems. At the same time, Django tries to stay out of your way, letting you work outside the scope of the framework as needed. We wrote this book because we firmly believe that Django makes Web development better. It’s designed to quickly get you moving on your own Django projects, and then ultimately teach you everything you need to know to successfully design, develop, and deploy a site that you’ll be proud of.

 

At its best, Web development is an exciting, creative act; at its worst, it can be a repetitive, frustrating nuisance. Django lets you focus on the fun stuff – the crux of your Web application – while easing the pain of the repetitive bits. In doing so, it provides high-level abstractions of common Web development patterns, shortcuts for frequent programming tasks, and clear conventions for how to solve problems. At the same time, Django tries to stay out of your way, letting you work outside the scope of the framework as needed.

 

First, developers of Django explains, in depth, what Django does and how to build Web applications with it. Second, we discuss higher-level concepts where appropriate, answering the question “How can I apply these tools effectively in my own projects?” By the Django book, you’ll learn the skills needed to develop powerful Web sites quickly, with code that is clean and easy to maintain.

 

Django’s History

 

Before we dive into more code, we should take a moment to explain Django’s history. We noted above that we’ll be showing you how to do things without shortcuts so that you more fully understand the shortcuts. Similarly, it’s useful to understand why Django was created, because knowledge of the history will put into context why Django works the way it does.

 

If you’ve been building Web applications for a while, you’re probably familiar with the problems in the CGI example we presented earlier. The classic Web developer’s path goes something like this:

 

1. Write a Web application from scratch.

2. Write another Web application from scratch.

3. Realize the application from step 1 shares much in common with the application from step 2.

4. Refactor the code so that application 1 shares code with application 2.

5. Repeat steps 2-4 several times.

6. Realize you’ve invented a framework.

 

This is precisely how Django itself was created!

 

Django grew organically from real-world applications written by a Web development team in Lawrence, Kansas, USA. It was born in the fall of 2003, when the Web programmers at the Lawrence Journal-Worldnewspaper, Adrian

 

Holovaty and Simon Willison, began using Python to build applications.

 

The World Online team, responsible for the production and maintenance of several local news sites, thrived in a development environment dictated by journalism deadlines. For the sites – including LJWorld.com, Lawrence.com and KUsports.com – journalists (and management) demanded that features be added and entire applications be built on an intensely fast schedule, often with only days‟ or hours‟ notice. Thus, Simon and Adrian developed a time-saving

 

Web development framework out of necessity – it was the only way they could build maintainable applications under the extreme deadlines.

 

In summer 2005, after having developed this framework to a point where it was efficiently powering most of World Online sites, the team, which now included Jacob Kaplan-Moss, decided to release the framework as open source software. They released it in July 2005 and named it Django, after the jazz guitarist Django Reinhardt.

 

Now, several years later, Django is a well-established open source project with tens of thousands of users and contributors spread across the planet. Two of the original World Online developers (the “Benevolent Dictators for Life,” Adrian and Jacob) still provide central guidance for the framework’s growth, but it’s much more of a collaborative team effort.

 

This history is relevant because it helps explain two key things. The first is Django’s “sweet spot.” Because Django was born in a news environment, it offers several features (such as its admin site, covered in Chapter 6) that are particularly well suited for “content” sites – sites like Amazon.com, craigslist.org, and washingtonpost.com that offer dynamic, database-driven information. Don’t let that turn you off, though – although Django is particularly good for developing those sorts of sites, that doesn’t preclude it from being an effective tool for building any sort of dynamic Web site. (There’s a difference between being particularly effective at something and being ineffective at other things.)

 

The second matter to note is how Django’s origins have shaped the culture of its open source community. Because Django was extracted from real-world code, rather than being an academic exercise or commercial product, it is acutely focused on solving Web development problems that Django’s developers themselves have faced – and continue to face. As a result, Django itself is actively improved on an almost daily basis. The framework’s maintainers have a vested interest in making sure Django saves developers time, produces applications that are easy to maintain and performs well under load. If nothing else, the developers are motivated by their own selfish desires to save themselves time and enjoy their jobs. (To put it bluntly, they eat their own dog food.)

3.3 SQLite

 

What is SQLite?

SQLite is a software library that implements a self-contained, serverless, zeroconfiguration, transactional SQL database engine. SQLite is the most widely deployed SQL database engine in the world. The source code for SQLite is in the public domain.

 

Android default Database engine is Lite. SQLite is a lightweight transactional database engine that occupies a small amount of disk storage and memory, so it's a perfect choice for creating databases on many mobile operating systems such as Android, iOS. It requires only little memory at runtime (approx. 250 KByte).

 

SQLite supports standard relational database features like SQL syntax, transactions and prepared statements.

 

SQLite supports the data types TEXT (similar to String in Java), INTEGER (similar to long in Java) and REAL (similar to double in Java). All other types must be converted into one of these fields before saving them in the database. SQLite itself does not validate if the types written to the columns are actually of the defined type, e.g. you can write an integer into a string column and vice versa.