Foreword for "Programming Python" (1st ed.)

As Python's creator, I'd like to say a few words about its origins, adding a bit of personal philosophy.

Over six years ago, in December 1989, I was looking for a "hobby" programming project that would keep me occupied during the week around Christmas. My office (a government-run research lab in Amsterdam) would be closed, but I had a home computer, and not much else on my hands. I decided to write an interpreter for the new scripting language I had been thinking about lately: a descendant of ABC that would appeal to Unix/C hackers. I chose Python as a working title for the project, being in a slightly irreverent mood (and a big fan of Monty Python's Flying Circus).

Today, I can safely say that Python has changed my life. I have moved to a different continent. I spend my working days developing large systems in Python, when I'm not hacking on Python or answering Python-related email. There are Python T-shirts, workshops, mailing lists, a newsgroup, and now a book. Frankly, my only unfulfilled wish is to have my picture on the front page of the New York Times. But before I get carried away daydreaming, here are a few tidbits from Python's past.

It all started with ABC, a wonderful teaching language that I had helped create in the early eighties. It was an incredibly elegant and powerful language, aimed at non-professional programmers. Despite all its elegance and power and the availability of a free implementation, ABC never became popular in the Unix/C world. I can only speculate about the reasons, but here's a likely one: the difficulty of adding new "primitive" operations to ABC. It was a monolithic, "closed system", with only the most basic I/O operations: read a string from the console, write a string to the console. I decided not repeat this mistake in Python.

Besides this intention, I had a number of other ideas for improvement over ABC, and was eager to try them out. For instance, ABC's powerful data types turned out to be less efficient than we hoped. There was too much emphasis on theoretically optimal algorithms, and not enough tuning for common cases. I also felt that some of ABC's features, aimed at novice programmers, were less desirable for the (then!) intended audience of experienced Unix/C programmers. For instance: ABC's ideosyncratic syntax (all uppercase keywords!); some terminology (e.g. "how-to" instead of "procedure"); and the integrated structured editor, which its users almost universally hated. Python would rely more on the Unix infrastructure and conventions, without being Unix-bound. And in fact, the first implementation was done on a Mac.

As it turned out, Python is remarkably free from many of the hang-ups of conventional programming languages. This is perhaps due to my choice of examples: besides ABC, my main influence was Modula-3. This is another language with remarkable elegance and power, designed by a small, strong-willed team (most of whom I had met during a summer internship at DEC's Systems Research Center in Palo Alto). Imagine what Python would have looked like if I had modelled it after the Unix shell and C instead! (Yes, I borrowed from C too, but only its least controversial features, in my desire to please the Unix/C audience.)

Any individual creation has its ideosyncracies, and occasionally its creator has to justify these. Perhaps Python's most controversial feature is its use of indentation for statement grouping, which derives directly from ABC. It is one of the language's features that is dearest to my heart. It makes Python code more readable in two ways. First, the use of indentation reduces visual clutter and makes programs shorter, thus reducing the attention span needed to take in a basic unit of code. Second, it allows the programmer less freedom in formatting, thereby enabling a more uniform style, which makes it easier to read someone else's code. (Compare, for instance, the three or four different conventions for the placement of braces in C, each with strong proponents.)

This emphasis on readability is no accident. As an object-oriented language, Python aims to encourage the creation of reusable code. Even if we all wrote perfect documentation all of the time, code can hardly be considered reusable if it's not readable. Many of Python's features, in addition to its use of indentation, conspire to make Python code highly readable. This reflects the philosophy of ABC, which was intended to teach programming in its purest form, and therefore placed a high value on clarity.

Readability is often enhanced by reducing unnecessary variability. When possible, there's a single, obvious way to code a particular construct. This reduces the number of choices facing the programmer who is writing the code, and increases the chance that will appear familiar to a second programmer reading it. Yet another contribution to Python's readability is the choice to use punctuation mostly in a conservative, conventional manner. Most operator symbols are familiar to anyone with even a vague recollection of high school math, and no new meanings have to be learned for comic strip curse characters like @&$!.

I will gladly admit that Python is not the fastest running scripting language. It is a good runner-up though. With ever-increasing hardware speed, the accumulated running time of a program during its lifetime is often negligible compared to the programmer time needed to write and debug it. This, of course, is where the real savings can be made. While this is hard to assess objectively, Python is considered a winner in coding time by most who have tried it. In addition, many consider using Python a pleasure -- a better recommendation is hard to imagine.

I am solely responsible for Python's strengths and shortcomings, even when some of the code has been written by others. However, its success is the product of a community, starting with the early adopters who picked it up when I first published Python on the net, and who spread the word about it in their own environment. They sent me their praise, criticism, feature requests, code contributions, and personal revelations via email. They were willing to discuss every aspect of Python in the mailing list that I soon set up, and educate me or nudge me in the right direction where my initial intuition failed me. There have been too many contributors to thank individually. I'll make one exception, however: this book's author was one of Python's early adopters and evangelists. With its publication, his longstanding wish (and mine!) of having a more accessible description of Python than the standard set of manuals, is fulfilled.

But enough rambling. I highly recommend this book to anyone interested in learning Python, whether for personal improvement or as a career enhancement. Take it away, Eric, the orchestra leader! (If you don't understand this last sentence, you haven't watched enough Monty Python reruns.)

Guido van Rossum
Reston, VA, May 1996