1.5 What Can I Do with Python?

Besides being a well-designed programming language, Python is also useful for accomplishing real world tasks—the sorts of things developers do day in and day out. It's commonly used in a variety of domains, as a tool for both scripting other components and implementing standalone programs. In fact, as a general purpose language, Python's roles are virtually unlimited.

However, the most common Python roles today seem to fall into a few broad categories. The next few sections describe some of Python's most common applications today, as well as tools used in each domain. We won't be able to describe all the tools mentioned here; if you are interested in any of these topics, see Python online or other resources for more details.

1.5.1 Systems Programming

Python's built-in interfaces to operating-system services make it ideal for writing portable, maintainable system-administration tools and utilities (sometimes called shell tools). Python programs can search files and directory trees, launch other programs, do parallel processing with processes and threads, and so on.

Python's standard library comes with POSIX bindings, and support for all the usual OS tools: environment variables, files, sockets, pipes, processes, multiple threads, regular expression pattern matching, command-line arguments, standard stream interfaces, shell-command launchers, filename expansion, and more. In addition, the bulk of Python's system interfaces are designed to be portable; for example, a script that copies directory trees typically runs unchanged on all major Python platforms.

1.5.2 GUIs

Python's simplicity and rapid turnaround also make it a good match for GUI (graphical user interface) programming. Python comes with a standard object-oriented interface to the Tk GUI API called Tkinter, which allows Python programs to implement portable GUIs with native look and feel. Python/Tkinter GUIs run unchanged on MS Windows, X Windows (on Unix and Linux), and Macs. A free extension package, PMW, adds advanced widgets to the base Tkinter toolkit. In addition, the wxPython GUI API, based on a C++ library, offers an alternative toolkit for constructing portable GUIs in Python.

Higher-level toolkits such as PythonCard and PMW are built on top of base APIs such as wxPython and Tkinter. With the proper library, you can also use other GUI toolkits in Python such as Qt, GTK, MFC, and Swing. For applications that run in web browsers or have simple interface requirements, both Jython and Python server-side CGI scripts provide additional user interface options.

1.5.3 Internet Scripting

Python comes with standard Internet modules that allow Python programs to perform a wide variety of networking tasks, in both client and server modes. Scripts can communicate over sockets; extract form information sent to a server-side CGI script; transfer files by FTP; process XML files; send, receive, and parse email; fetch web pages by URLs; parse the HTML and XML of fetched web pages; communicate over XML-RPC, SOAP, and telnet; and more. Python's libraries make these tasks remarkably simple.

In addition, there is a large collection of third party tools on the web for doing Internet programming in Python. For instance, the HTMLGen system generates HTML files from Python class-based descriptions; the win32all Windows extensions package allows Python code to be embedded in HTML files in the spirit of JavaScript; the mod_python package runs Python efficiently within the Apache web server; and the Jython system provides for seamless Python/Java integration, and supports coding of server-side applets that run on clients. In addition, full-blown web development packages for Python such as Zope, WebWare, and Quixote, support quick construction of web sites.

1.5.4 Component Integration

We discussed the component integration role earlier, when describing Python as a control language. Python's ability to be extended by and embedded in C and C++ systems makes it useful as a flexile glue language, for scripting the behavior of other systems and components. For instance, by integrating a C library into Python, Python can test and launch its components. And by embedding Python in a product, on-site customizations can be coded without having to recompile the entire product, or ship its source code at all.

Tools such as the SWIG code generator can automate much of the work needed to link compiled components into Python for use in scripts. And larger frameworks such as Python's COM support on MS Windows, the Jython Java-based implementation, the Python.NET system, and various CORBA toolkits for Python provide alternative ways to script components. On Windows, for example, Python scripts can use frameworks to script MS Word and Excel, and serve the same sorts of roles as Visual Basic.

1.5.5 Database Programming

Python's standard pickle module provides a simple object persistence system—it allows programs to easily save and restore entire Python objects to files and file-like objects. For more traditional database demands, there are Python interfaces to Sybase, Oracle, Informix, ODBC, MySQL, and more.

The Python world has also defined a portable database API for accessing SQL database systems from Python scripts, which looks the same on a variety of underlying database systems. For instance, because vendor interfaces implement the portable API, a script written to work with the free MySQL system will work largely unchanged on other systems such as Oracle by simply replacing the underlying vendor interface. On the web, you'll also find a third-party system named gadfly that implements a SQL database for Python programs, a complete object-oriented database system called ZODB.

1.5.6 Rapid Prototyping

To Python programs, components written in Python and C look the same. Because of this, it's possible to prototype systems in Python initially and then move components to a compiled language such as C or C++ for delivery. Unlike some prototyping tools, Python doesn't require a complete rewrite once the prototype has solidified. Parts of the system that don't require the efficiency of a language such as C++ can remain coded in Python for ease of maintenance and use.

1.5.7 Numeric Programming

The NumPy numeric programming extension for Python mentioned earlier includes such advanced tools as an array object, interfaces to standard mathematical libraries, and much more. By integrating Python with numeric routines coded in a compiled language for speed, NumPy turns Python into a sophisticated yet easy-to-use numeric programming tool, which can often replace existing code written in traditional compiled languages such as FORTRAN or C++. Additional numeric tools for Python support animation, 3D visualization, and so on.

1.5.8 Gaming, Images, AI, XML, and More

Python is commonly applied in more domains than can be mentioned here. For example, you can do graphics and game programming in Python with the pygame system; image processing with the PIL package and others; AI programming with neural network simulators and expert system shells; XML parsing with the xml library package, the xmlrpclib module, and third-party extensions; and even play solitaire with the PySol program. You'll find support for many such fields at the Vaults of Parnassus web site (linked from http://www.python.org). (The Vaults of Parnassus is a large collection of links to third-party software for Python programming. If you need to do something special with Python, the Vaults is usually the best first place to look for resources.)

In general, many of these specific domains are largely just instances of Python's component integration role in action again. By adding Python as a frontend to libraries of components written in a compiled language such as C, Python becomes useful for scripting in a wide variety of domains. As a general purpose language that supports integration, Python is widely applicable.