Exploring Python (2009).pdf

Exploring Python

Timothy A. Budd

Exploring Python – Preface

Preface

To the student: Why Python?

Given so many other programming languages in the world, why should you learn Python

as your first exposure to computer programming? Well, the real answer is that your

instructor selected the both the language and this textbook for the course, so what choice

do you have? Nonetheless, let me explain why this was a very good decision.

Python is easy, Python is fun, Python is educational, and Python is powerful.

Let’s start with the powerful. If you look at the case studies toward the end of the book,

you will see that you will end up learning how to do some very interesting things. Tasks

like writing your own blog, automatically solving soduko puzzles, reading your iTunes

database, or writing a wiki. None of these take more than a page or two of Python code.

This is considerably smaller than the equivalent programs would be in almost any other

programming language.

Is it easy? Let me fudge and say it is eas ier . Computer programming in any language

takes skill, organization, logic, and patience. Python is no different in this regard. What

makes Python attractive is that you can begin so quickly and easily. Your first Python

program can be as simple as 2 + 3:

>>> 2 + 3

Thereafter the path to learning how to create your own complex applications is, we hope,

at least clearly laid out, even if it will take some effort on your part.

Active Learning

This book follows an attitude towards teaching that has been termed active learning .

Rather than treating you, the student, as a passive repository into which knowledge is

poured, active learning tries to engage you, the student, as a fully equal partner in the

process of learning. Rather than simply telling you how some feature works, I will

usually suggest experiments that you can perform to discover the answer on your own.

There are several benefits to this approach. First, it makes you use a different part of your

brain than you would if you were simply reading. Second, it gives you, the student, a

greater sense of ownership of the knowledge. Third, experimentation is often the fun part

of programming. Lastly, by encouraging you to experiment in the discovery of simple

information, I hope to instill habits that you will continue to carry with you throughout

your programming career. Together, the intent is that active learning helps you more

easily retain and use the information you have learned.

Exploring Python – Preface

What is Python?

For those looking for buzzwords, Python is a high-level, interpreted, reflective,

dynamically-typed, open-source, multi-paradigm, general-purpose programming

language. I could explain each of those terms in detail, but in the end the result would

still not convey what makes Python programming different from other languages. There

is no one thing in Python that is not found in other languages, but it is the elegant design

and combination of these features into a single package that makes Python such a

pleasure to use.

Python is sometimes described as a scripting language , for the simple reason that

thousands of working programmers daily use the language in this fashion. That is, they

use Python as a tool to quickly and easily glue together software applications and

components written in many different languages. But such a categorization is far too

narrow, and Python can justly be described as a general-purpose language, one that can

you can use for almost any programming task you would like to perform.

This is not to say that Python is the only programming language you will ever need or

will ever learn. A working computer scientist should know how to use many different

tools, and that means he or she should have an appreciation of many different types of

language. For example, because Python is interpreted, the resulting programs are often

not as fast as those written in lower-level languages, such as C or C++. On the other

hand, programs are much easier to write than they are in C. So there is a trade-off, an

engineering compromise of the type common in computer science. Is less time in

execution of the final program worth spending more time in development and debugging?

For the beginning student, and in fact for the vast majority of computer programs, the

answer is clearly no. (Another way to express this trade-off is to ask, “whose time is more

important, your time or the computer’s?”) Low-level languages such as C have their

place, but only for the small group of computer programs for which ultimate execution

time is critically important. You may eventually work on such systems, but not in your

first programming course.

Another important category of programming languages are those tied to a specific

application. A good example of this category is the language PHP, a programming

language used to create interactive web pages. (See www.php.org ). A general-purpose

language, such as Python, cannot hope to be as easy to use in this application area. But

PHP is extremely clumsy to use for purposes other than web pages. If, or when, you start

extensive work in such an application area you will want to learn how to use these tools.

Bottom line, Python is an excellent place to start. And to stay, for many of your

programming tasks. But you should not assume that it is the last language you will ever

need or learn. Fortunately, languages have many features in common with each other. A

solid foundation in one language (such as Python) makes it much easier to learn a second

Exploring Python – Preface

(or third, or forth). An appendix at the back of this book provides hints as to how one

should approach the task of learning a new language.

History of Python

Python was designed by Guido van Rossum while he was working at the CWI (the

Centrum voor Wiskunke and Informatica; literally “center for wisdom and informatics”)

a world-class research lab in the Netherlands. The CWI group he was associated with

designed a programming language called ABC. I was fortunate to spend a year with this

group in 1985. ABC was clearly intended as a pedagogical tool for teaching

programming, and a great deal of work went into developing both the language and

associated teaching material. 1 The language ABC had a number of features that were

impressive for the time: a tightly integrated development environment, interactive

execution, high level data types (lists, dictionaries, tuples and strings), dynamic memory

management, strong typing without declaration statements and more. The idea to use

indentation for nesting, and eliminate the brackets or BEGIN/END keywords found in

most other languages, was taken directly from ABC. So was the idea of dynamic typing.

Software development in ABC was both rapid and enjoyable, and totally unlike almost

any other competing language. (The one exception might be Smalltalk, which was just

becoming well known in 1985. Indeed, during my time at the CWI I was writing a book

on Smalltalk, and part of the work I performed during that year was to explain to my

colleagues in the ABC group the basic ideas of Object-Oriented programming, which I

myself was only just beginning to understand).

Guido started designing Python around 1990. For those familiar with the earlier language

the heritage of ABC in Python is clear. Guido discarded some of the annoying features of

ABC, and kept all the best ideas, recasting them in the form of a more general-purpose

language. By then the mechanisms of object-oriented programming were well

understood, and the language included all the latest features. He added a number of

features not found in ABC, such as a system for modularization and including libraries of

useful utilities. Python was released to the world in 1991, and very quickly attracted a

loyal following. Python’s design turned out to be general enough to address a much wider

range of applications than ABC. (To be fair, the designers of ABC were focused on

teaching, and never intended the language to be general-purpose). The features that

programmers appreciated in 1990 are still the same today: ease of use, rapid software

development, the right set of data types that help to quickly address most common

programming problems.

Python, Monty

1 See the Wikipedia entry on ABC for further discussion of this language. The Wikipedia

entry for Python has a much more complete history of the language. There is also a

Wikipedia entry that explains the concepts of active learning. Wikipedia is found on the

web at www.wikipedia.org.

Exploring Python – Preface

The name, by the way, owes nothing to the reptile and everything to the 1970’s BBC

comedy series Monty Python’s Flying Circus . Many die-hard Python programmers enjoy

making sly references to this series in their examples. You don’t need to have seen Monty

Python’s Life of Brian, The Meaning of Life, And Now for something Completely

Different, or Monty Python and the Holy Grail or even Spamalot in order to become a

Python programmer, but it can’t hurt, either.

To the Instructor

I will begin this section with the same question I used at the start of the preface to the

students. Why is Python a better programming language for the first course than, say, C,

C++, Java, C#, Delphi, Ada, or Eiffel, just to name a few alternatives? The answer, as I

suggested earlier, is that students will find that Python provides a much easier entrance

into the world of programming, yet is complete enough to provide a comprehensive

introduction to all the important ideas in programming, and is fun to use.

The fact that Python can be used in both an interactive and textual style makes the barrier

for the beginning student extremely low. This is not true for other languages. To write

even the simplest Java program, for example, the instructor must explain (or worse, not

explain and leave as a magic incantation) ideas such as classes, functions, standard input,

static variables, arrays, strings, and more. In contrast, the first Python program can be as

simple as 2 + 3:

>>> 2 + 3

The positive influence of interactive execution for the beginning student cannot be

overstated. It permits (and the conscientious instructor should encourage) an exploratory

and active approach to learning. To find out how something works, try it out! This

empowers the student to take control of his or her own voyage of discovery, instead of

simply playing the role of a passive container into which the instructor (or the book)

pours information. I have discussed this active learning approach in my earlier remarks

for the student.

But the fact that simple things are easy to write in Python should not be an excuse to

imagine that the language is just a toy. It is a credit to the good design skills of Guido van

Rossum (the language designer) and countless others that simple ideas are simple to

express, and complex ideas can also be illustrated with simple examples. In what other

language might an introductory textbook include examples of a blog, a wiki, or an XML

parser?

Python is also an excellent vehicle for teaching computer science. All the basic concepts

of programming (ideas such as values, variables, types, statements, conditionals, loops,

functions, recursion, classes, inheritance, just to name a few) can be found in Python. The

student gaining experience with these topics in this language is therefore in an excellent

position to more easily learn other languages at a later time. An appendix offers some

Exploring Python – Preface

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: