If you've bought this book, you may already know what Python is, and why it's an important tool to learn. If you don't, you probably won't be sold on Python until you've learned the language by reading the rest of this book and have done a project or two. But before we jump into details, the first few pages of this book will briefly introduce some of the main reasons behind Python's popularity. To begin sculpting a definition of Python, this chapter takes the form of a question-and-answer session, which poses some of the most common questions asked by beginners.
Because there are many programming languages available today, this is the usual first question of newcomers. Given that there are roughly 1 million Python users out there at the moment, there really is no way to answer this question with complete accuracy. The choice of development tools is sometimes based on unique constraints or personal preference.
But after teaching Python to roughly 200 groups and 3,000 students during the last 10 years, some common themes have emerged. The primary factors cited by Python users seem to be these:
For many, Python's focus on readability, coherence, and software quality in general sets it apart from other tools in the scripting world. Python code is designed to be readable, and hence, reusable and maintainable—much more so than traditional scripting languages. The uniformity of Python code makes it easy to understand, even if you did not write it. In addition, Python has deep support for more advanced software reuse mechanisms, such as object-oriented programming (OOP).
Python boosts developer productivity many times beyond compiled or statically typed languages such as C, C++, and Java. Python code is typically one-third to one-fifth the size of equivalent C++ or Java code. That means there is less to type, less to debug, and less to maintain after the fact. Python programs also run immediately, without the lengthy compile and link steps of some other tools, further boosting programmer speed.
Most Python programs run unchanged on all major computer platforms. Porting Python code between Linux and Windows, for example, is usually just a matter of copying a script's code between machines. Moreover, Python offers multiple options for coding portable graphical user interfaces, database access programs, web-based systems, and more. Even operating system interfaces, including program launches and directory processing, are as portable in Python as they can possibly be.
Python comes with a large collection of prebuilt and portable functionality, known as the standard library. This library supports an array of application-level programming tasks, from text pattern matching to network scripting. In addition, Python can be extended with both homegrown libraries and a vast collection of third-party application support software. Python's third-party domain offers tools for web site construction, numeric programming, serial port access, game development, and much more. The NumPy extension, for instance, has been described as a free and more powerful equivalent to the Matlab numeric programming system.
Python scripts can easily communicate with other parts of an application, using a variety of integration mechanisms. Such integrations allow Python to be used as a product customization and extension tool. Today, Python code can invoke C and C++ libraries, can be called from C and C++ programs, can integrate with Java components, can communicate over frameworks such as COM and .NET, and can interact over networks with interfaces like SOAP, XML-RPC, and CORBA. It is not a standalone tool.
Because of Python's ease of use and built-in toolset, it can make the act of programming more pleasure than chore. Although this may be an intangible benefit, its effect on productivity is an important asset.
Of these factors, the first two (quality and productivity) are probably the most compelling benefits to most Python users.
By design, Python implements a deliberately simple and readable syntax, and a highly coherent programming model. As a slogan at a recent Python conference attests, the net result is that Python seems to "fit your brain"—that is, features of the language interact in consistent and limited ways, and follow naturally from a small set of core concepts. This makes the language easier to learn, understand, and remember. In practice, Python programmers do not need to constantly refer to manuals when reading or writing code; it's a consistently designed system that many find yields surprisingly regular-looking code.
By philosophy, Python adopts a somewhat minimalist approach. This means that although there are usually multiple ways to accomplish a coding task, there is usually just one obvious way, a few less obvious alternatives, and a small set of coherent interactions everywhere in the language. Moreover, Python doesn't make arbitrary decisions for you; when interactions are ambiguous, explicit intervention is preferred over "magic." In the Python way of thinking, explicit is better than implicit, and simple is better than complex.
Beyond such design themes, Python includes tools such as modules and OOP that naturally promote code reusability. And because Python is focused on quality, so too, naturally, are Python programmers.
During the great Internet boom of the mid-to-late 1990s, it was difficult to find enough programmers to implement software projects; developers were asked to implement systems as fast as the Internet evolved. Now, in the post-boom era of layoffs and economic recession, the picture has shifted. Today, programming staffs are often asked to accomplish the same tasks with even fewer people.
In both of these scenarios, Python has shined as a tool that allows programmers to get more done with less effort. It is deliberately optimized for speed of development—its simple syntax, dynamic typing, lack of compile steps, and built-in toolset allow programmers to develop programs in a fraction of the time needed when using some other tools. The net effect is that Python typically boosts developer productivity many times beyond the levels supported by traditional languages. That's good news in both boom and bust times, and everywhere the software industry goes in between.
Python is a general-purpose programming language that is often applied in scripting roles. It is commonly defined as an object-oriented scripting language—a definition that blends support for OOP with an overall orientation toward scripting roles. In fact, people often use the word "script" instead of "program" to describe a Python code file. In this book, the terms "script" and "program" are used interchangeably, with a slight preference for "script" to describe a simpler top-level file, and "program" to refer to a more sophisticated multifile application.
Because the term "scripting language" has so many different meanings to different observers, some would prefer that it not be applied to Python at all. In fact, people tend to make three very different associations, some of which are more useful than others, when they hear Python labeled as such:
Sometimes when people hear Python described as a scripting language, they think it means that Python is a tool for coding operating-system-oriented scripts. Such programs are often launched from console command lines, and perform tasks such as processing text files and launching other programs.
To others, scripting refers to a "glue" layer used to control and direct (i.e., script) other application components. Python programs are indeed often deployed in the context of larger applications. For instance, to test hardware devices, Python programs may call out to components that give low-level access to a device. Similarly, programs may run bits of Python code at strategic points to support end-user product customization without having to ship and recompile the entire system's source code.
Python's simplicity makes it a naturally flexible control tool. Technically, though, this is also just a common Python role; many Python programmers code standalone scripts without ever using or knowing about any integrated components. It is not just a control language.
Probably the best way to think of the term "scripting language" is that it refers to a simple language used for quickly coding tasks. This is especially true when the term is applied to Python, which allows much faster program development than compiled languages like C++. Its rapid development cycle fosters an exploratory, incremental mode of programming that has to be experienced to be appreciated.
Don't be fooled, though—Python is not just for simple tasks. Rather, it makes tasks simple by its ease of use and flexibility. Python has a simple feature set, but it allows programs to scale up in sophistication as needed. Because of that, it is commonly used for quick tactical tasks and longer-term strategic development.
So, is Python a scripting language or not? It depends on whom you ask. In general, the term "scripting" is probably best used to describe the rapid and flexible mode of development that Python supports, rather than a particular application domain.
After using Python for 15 years and teaching it for 10, the only downside to Python I've found is that, as currently implemented, its execution speed may not always be as fast as compiled languages such as C and C++.
We'll talk about implementation concepts in detail later in this book. In short, the standard implementations of Python today compile (i.e., translate) source code statements to an intermediate format known as byte code, and then interpret the byte code. Byte code provides portability, as it is a platform-independent format. However, because Python is not compiled all the way down to binary machine code (e.g., instructions for an Intel chip), some programs will run more slowly in Python than in a fully compiled language like C.
Whether you will ever care about the execution speed difference depends on what kinds of programs you write. Python has been optimized numerous times, and Python code runs fast enough by itself in most application domains. Furthermore, whenever you do something "real" in a Python script, like process a file or construct a GUI, your program is actually running at C speed, since such tasks are immediately dispatched to compiled C code inside the Python interpreter. More fundamentally, Python's speed-of-development gain is often far more important than any speed-of-execution loss, especially given modern computer speeds.
Even at today's CPU speeds, though, there still are some domains that do require optimal execution speeds. Numeric programming and animation, for example, often need at least their core number-crunching components to run at C speed (or better). If you work in such a domain, you can still use Python—simply split off the parts of the application that require optimal speed into compiled extensions, and link those into your system for use in Python scripts.
We won't talk about extensions much in this text, but this is really just an instance of the Python-as-control-language role that we discussed earlier. A prime example of this dual language strategy is the NumPy numeric programming extension for Python; by combining compiled and optimized numeric extension libraries with the Python language, NumPy turns Python into a numeric programming tool that is efficient and easy to use. You may never need to code such extensions in your own Python work, but they provide a powerful optimization mechanism if you ever do.
At this writing, in 2007, the best estimate anyone can seem to make of the size of the Python user base is that there are roughly 1 million Python users around the world today (plus or minus a few). This estimate is based on various statistics, like download rates and developer surveys. Because Python is open source, a more exact count is difficult—there are no license registrations to tally. Moreover, Python is automatically included with Linux distributions, Macintosh computers, and some products and hardware, further clouding the user-base picture.
In general, though, Python enjoys a large user base, and a very active developer community. Because Python has been around for more than 15 years and has been widely used, it is also very stable and robust. Besides being employed by individual users, Python is also being applied in real revenue-generating products by real companies. For instance:
Google makes extensive use of Python in its web search system, and employs Python's creator.
The YouTube video sharing service is largely written in Python.
The popular BitTorrent peer-to-peer file sharing system is a Python program.
Intel, Cisco, Hewlett-Packard, Seagate, Qualcomm, and IBM use Python for hardware testing.
Industrial Light & Magic, Pixar, and others use Python in the production of movie animation.
JPMorgan Chase, UBS, Getco, and Citadel apply Python for financial market forecasting.
NASA, Los Alamos, Fermilab, JPL, and others use Python for scientific programming tasks.
iRobot uses Python to develop commercial robotic vacuum cleaners.
ESRI uses Python as an end-user customization tool for its popular GIS mapping products.
The NSA uses Python for cryptography and intelligence analysis.
The IronPort email server product uses more than 1 million lines of Python code to do its job.
The One Laptop Per Child (OLPC) project builds its user interface and activity model in Python.
And so on. Probably the only common thread amongst the companies using Python today is that Python is used all over the map, in terms of application domains. Its general-purpose nature makes it applicable to almost all fields, not just one. In fact, it's safe to say that Python is being used by virtually every substantial organization writing software, whether for short-term tactical tasks such as testing and administration, or for long-term strategic product development. Python has proven to work well in both modes.
For more details on companies using Python today, see Python's web site at http://www.python.org.
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 scripting other components and implementing standalone programs. In fact, as a general-purpose language, Python's roles are virtually unlimited: you can use it for everything from web site development and gaming, to robotics and spacecraft control.
However, the most common Python roles currently 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 explore the tools mentioned here in any depth—if you are interested in any of these topics, see the Python web site, or other resources for more details.
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.
Python's simplicity and rapid turnaround also make it a good match for graphical user interface (GUI) 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 a native look and feel. Python/Tkinter GUIs run unchanged on MS Windows, X Windows (on Unix and Linux), and the Mac OS (both Classic and OS X). A free extension package, PMW, adds advanced widgets to the 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 Dabo 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 (the Java version of Python, described in Chapter 2) and Python server-side CGI scripts provide additional user interface options.
Python comes with standard Internet modules that allow Python programs to perform a wide variety of networking tasks, in client and server modes. Scripts can communicate over sockets; extract form information sent to server-side CGI scripts; transfer files by FTP; process XML files; send, receive, compose, 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 available on the Web for doing Internet programming in Python. For instance, the HTMLGen system generates HTML files from Python class-based descriptions, the mod_python package runs Python efficiently within the Apache web server and supports server-side templating with its Python Server Pages, 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 Django, TurboGears, Pylons, Zope, and WebWare, support quick construction of full-featured and production-quality web sites with Python.
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 flexible glue language for scripting the behavior of other systems and components. For instance, integrating a C library into Python enables Python to test and launch the library's components, and embedding Python in a product enables onsite customizations to be coded without having to recompile the entire product, or ship its source code at all.
Tools such as the SWIG and SIP code generators 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 IronPython .NET-based implementation, 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.
For traditional database demands, there are Python interfaces to all commonly used relational database systems—Sybase, Oracle, Informix, ODBC, MySQL, PostgreSQL, SQLite, 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); all you have to do is replace the underlying vendor interface.
provides a simple object persistence system—it
allows programs to easily save and restore entire Python objects to
files and file-like objects. On the Web, you'll also find a third-party
system named ZODB that provides a complete object-oriented database
system for Python scripts, and another called SQLObject that maps
relational tables onto Python's class model. And, as of Python 2.5,
SQLite is a standard part of Python itself.
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 selected 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.
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, parallel processing, and so on.
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; robot control programming
with the PyRo toolkit; XML parsing with the
xml library package, the
xmlrpclib module, and third-party extensions;
AI programming with neural network simulators and expert system shells;
and natural language analysis with the NLTK
package. You can even play solitaire with the PySol
program. You'll find support for many such fields at the Vaults of
Parnassus, and the newer PyPI web sites (search Google or http://www.python.org for links).
In general, many of these specific domains are largely just instances of Python's component integration role in action again. Adding Python as a frontend to libraries of components written in a compiled language such as C makes Python useful for scripting in a wide variety of domains. As a general-purpose language that supports integration, Python is widely applicable.
Naturally, this is a developer's question. If you don't already have a programming background, the language in the next few sections may be a bit baffling—don't worry, we'll explore all of these terms in more detail as we proceed through this book. For developers, though, here is a quick introduction to some of Python's top technical features.
Python is an object-oriented language, from the ground up. Its class model supports advanced notions such as polymorphism, operator overloading, and multiple inheritance; yet, in the context of Python's simple syntax and typing, OOP is remarkably easy to apply. In fact, if you don't understand these terms, you'll find they are much easier to learn with Python than with just about any other OOP language available.
Besides serving as a powerful code structuring and reuse device, Python's OOP nature makes it ideal as a scripting tool for object-oriented systems languages such as C++ and Java. For example, with the appropriate glue code, Python programs can subclass (specialize) classes implemented in C++, Java, and C#.
Of equal significance, OOP is an option in Python; you can go far without having to become an object guru all at once. Much like C++, Python supports both procedural and object-oriented programming modes. Its object-oriented tools can be applied if and when constraints allow. This is especially useful in tactical development modes, which preclude design phases.
Python is completely free to use and distribute. As with other open source software, such as Tcl, Perl, Linux, and Apache, you can fetch the entire Python system's source code for free on the Internet. There are no restrictions on copying it, embedding it in your systems, or shipping it with your products. In fact, you can even sell Python's source code, if you are so inclined.
But don't get the wrong idea: "free" doesn't mean "unsupported." On the contrary, the Python online community responds to user queries with a speed that most commercial software vendors would do well to notice. Moreover, because Python comes with complete source code, it empowers developers, leading to the creation of a large team of implementation experts. Although studying or changing a programming language's implementation isn't everyone's idea of fun, it's comforting to know that it's available as a final resort and ultimate documentation source. You're not dependent on the whims of a commercial vendor.
Python development is performed by a community, which largely coordinates its efforts over the Internet. It consists of Python's creator—Guido van Rossum, the officially anointed Benevolent Dictator for Life (BDFL) of Python—plus a cast of thousands. Language changes must follow a formal enhancement procedure (known as the PEP process), and be scrutinized by a formal testing system and the BDFL. Happily, this tends to make Python more conservative with changes than some other languages.
The standard implementation of Python is written in portable ANSI C, and it compiles and runs on virtually every major platform currently in use. For example, Python programs run today on everything from PDAs to supercomputers. As a partial list, Python is available on:
Linux and Unix systems
Microsoft Windows and DOS (all modern flavors)
Mac OS (both OS X and Classic)
BeOS, OS/2, VMS, and QNX
Real-time systems such as VxWorks
Cray supercomputers and IBM mainframes
PDAs running Palm OS, PocketPC, and Linux
Cell phones running Symbian OS and Windows Mobile
Gaming consoles and iPods
Besides the language interpreter itself, the standard library modules that ship with Python are also implemented to be as portable across platform boundaries as possible. Further, Python programs are automatically compiled to portable byte code, which runs the same on any platform with a compatible version of Python installed (more on this in the next chapter).
What that means is that Python programs using the core language and standard libraries run the same on Linux, Windows, and most other systems with a Python interpreter. Most Python ports also contain platform-specific extensions (e.g., COM support on Windows), but the core Python language and libraries work the same everywhere. As mentioned earlier, Python also includes an interface to the Tk GUI toolkit called Tkinter, which allows Python programs to implement full-featured graphical user interfaces that run on all major GUI platforms without program changes.
From a features perspective, Python is something of a hybrid. Its toolset places it between traditional scripting languages (such as Tcl, Scheme, and Perl), and systems development languages (such as C, C++, and Java). Python provides all the simplicity and ease of use of a scripting language, along with more advanced software-engineering tools typically found in compiled languages. Unlike some scripting languages, this combination makes Python useful for large-scale development projects. As a preview, here are some of the main things you'll find in Python's toolbox:
Python keeps track of the kinds of objects your program uses when it runs; it doesn't require complicated type and size declarations in your code. In fact, as you'll see in Chapter 6, there is no such thing as a type or variable declaration anywhere in Python. Because Python code does not constrain data types, it is also usually automatically applicable to a whole range of objects.
Python automatically allocates objects and reclaims ("garbage collects") them when they are no longer used, and most grow and shrink on demand. As you'll learn, Python keeps track of low-level memory details so you don't have to.
For building larger systems, Python includes tools such as modules, classes, and exceptions. These tools allow you to organize systems into components, use OOP to reuse and customize code, and handle events and errors gracefully.
Python provides commonly used data structures such as lists, dictionaries, and strings as intrinsic parts of the language; as you'll see, they're both flexible and easy to use. For instance, built-in objects can grow and shrink on demand, can be arbitrarily nested to represent complex information, and more.
For more specific tasks, Python also comes with a large collection of precoded library tools that support everything from regular-expression matching to networking. Python's library tools are where much of the application-level action occurs.
Because Python is open source, developers are encouraged to contribute precoded tools that support tasks beyond those supported by its built-ins; on the Web, you'll find free support for COM, imaging, CORBA ORBs, XML, database access, and much more.
Despite the array of tools in Python, it retains a remarkably simple syntax and design. The result is a powerful programming tool with all the usability of a scripting language.
Python programs can easily be "glued" to components written in other languages in a variety of ways. For example, Python's C API lets C programs call and be called by Python programs flexibly. That means you can add functionality to the Python system as needed, and use Python programs within other environments or systems.
Mixing Python with libraries coded in languages such as C or C++, for instance, makes it an easy-to-use frontend language and customization tool. As mentioned earlier, this also makes Python good at rapid prototyping; systems may be implemented in Python first, to leverage its speed of development, and later, moved to C for delivery, one piece at a time, according to performance demands.
To run a Python program, you simply type it and run it. There are no intermediate compile and link steps, like there are for languages such as C or C++. Python executes programs immediately, which makes for an interactive programming experience and rapid turnaround after program changes—in many cases, you can witness the effect of a program change as fast as you can type it.
Of course, development cycle turnaround is only one aspect of Python's ease of use. It also provides a deliberately simple syntax and powerful built-in tools. In fact, some have gone so far as to call Python "executable pseudocode." Because it eliminates much of the complexity in other tools, Python programs are simpler, smaller, and more flexible than equivalent programs in languages like C, C++, and Java!
This brings us to a key point of this book: compared to other programming languages, the core Python language is remarkably easy to learn. In fact, you can expect to be coding significant Python programs in a matter of days (or perhaps in just hours, if you're already an experienced programmer). That's good news for professional developers seeking to learn the language to use on the job, as well as for end users of systems that expose a Python layer for customization or control. Today, many systems rely on the fact that end users can quickly learn enough Python to tailor their Python customizations' code onsite, with little or no support. Although Python does have advanced programming tools, its core language is still simple for beginners and gurus alike.
OK, this isn't quite a technical strength, but it does seem to be a surprisingly well-kept secret that I wish to expose up front. Despite all the reptile icons in the Python world, the truth is that Python creator Guido van Rossum named it after the BBC comedy series Monty Python's Flying Circus. He is a big fan of Monty Python, as are many software developers (indeed, there seems to almost be a symmetry between the two fields).
This legacy inevitably adds a humorous quality to Python code examples. For instance, the traditional "foo" and "bar" for generic variable names become "spam" and "eggs" in the Python world. The occasional "Brian," "ni," and "shrubbery" likewise owe their appearances to this namesake. It even impacts the Python community at large: talks at Python conferences are regularly billed as "The Spanish Inquisition."
All of this is, of course, very funny if you are familiar with the show, but less so otherwise. You don't need to be familiar with the series to make sense of examples that borrow references to Monty Python (including many you will see in this book), but at least you now know their root.
Finally, to place it in the context of what you may already know, people sometimes compare Python to languages such as Perl, Tcl, and Java. We talked about performance earlier, so here we'll focus on functionality. While other languages are also useful tools to know and use, many people find that Python:
Is more powerful than Tcl. Python's support for "programming in the large" makes it applicable to the development of larger systems.
Has a cleaner syntax and simpler design than Perl, which makes it more readable and maintainable, and helps reduce program bugs.
Is simpler and easier to use than Java. Python is a scripting language, but Java inherits much of the complexity and syntax of systems languages such as C++.
Is simpler and easier to use than C++, but often doesn't compete with C++, either; as a scripting language, Python often serves different roles.
Is both more powerful and more cross-platform than Visual Basic. Its open source nature also means it is not controlled by a single company.
Is more mature and has a more readable syntax than Ruby. Unlike Ruby and Java, OOP is an option in Python—Python does not impose OOP on users or projects to which it may not apply.
Has the dynamic flavor of languages like SmallTalk and Lisp, but also has a simple, traditional syntax accessible to developers as well as end users of customizable systems.
Especially for programs that do more than scan text files, and that might have to be read in the future by others (or by you!), many people find that Python fits the bill better than any other scripting or programming language available today. Furthermore, unless your application requires peak performance, Python is often a viable alternative to systems development languages such as C, C++, and Java: Python code will be much less difficult to write, debug, and maintain.
Of course, your author has been a card-carrying Python evangelist since 1992, so take these comments as you may. They do, however, reflect the common experience of many developers who have taken time to explore what Python has to offer.
And that concludes the hype portion of this book. In this chapter, we've explored some of the reasons that people pick Python for their programming tasks. We've also seen how it is applied, and a representative sample of who is using it today. My goal is to teach Python, though, not to sell it. The best way to judge a language is to see it in action, so the rest of this book focuses entirely on the language details we've glossed over here.
To get started, the next two chapters begin our technical introduction to the language. There, we explore ways to run Python programs, peek at Python's byte code execution model, and introduce the basics of module files for saving code. The goal will be to give you just enough information to run the examples and exercises in the rest of the book. You won't really start programming until Chapter 4, but make sure you have a handle on the startup details before moving on.
In this edition of the book, we will be closing each chapter with a quick pop quiz about the material presented to help you review the key concepts. The answers for these quizzes appear immediately after the questions, and you are encouraged to read the answers once you've taken a crack at the questions yourself. In addition to these end-of-chapter quizzes, you'll find lab exercises at the end of each part of the book, designed to help you start coding Python on your own. For now, here's your first test. Good luck!
What are the six main reasons that people choose to use Python?
Name four notable companies or organizations using Python today.
Why might you not want to use Python in an application?
What can you do with Python?
What's the significance of the Python
Why does "spam" show up in so many Python examples in books and on the Web?
What is your favorite color?
How did you do? Here are the answers I came up with, though there may be multiple solutions to some quiz questions. Again, even if you're sure you got a question right, I encourage you to look at these answers for additional context. See the chapter's text for more details if any of these responses don't make sense to you.
Software quality, developer productivity, program portability, support libraries, component integration, and enjoyment. Of these, the quality and productivity themes seem to be the main reasons that people choose to use Python.
Google, Industrial Light & Magic, Jet Propulsion Labs, ESRI, and many more. Almost every organization doing software development is using Python in some fashion, whether for long-term strategic product development, or for short-term tactical tasks such as testing and system administration.
Python's downside is performance: it won't run as quickly as fully compiled languages like C and C++. On the other hand, it's quick enough for most applications, and typical Python code runs at close to C speed anyhow because it invokes linked-in C code in the interpreter. If speed is critical, compiled extensions are available for number-crunching parts of an application.
You can use Python for nearly anything you can do with a computer—from web site development and gaming, to robotics and spacecraft control.
"Spam" is a reference from a famous Monty Python skit in which people trying to order food in a cafeteria are drowned out by a chorus of Vikings singing about spam. Oh, and it's also a common variable name in Python scripts . . . .
Blue. No, yellow!
 * For a more complete look at the
Python philosophy, type the command
this at any Python interactive prompt (you'll see how in
Chapter 2). This invokes an
"Easter egg" hidden in Python—a collection of design principles
underlying Python. The acronym EIBTI is now fashionable jargon for
the "explicit is better than implicit" rule.