MCGraw-Hill Osborne Exploring Python (2009), ebooks, Python Programming eBooks Collection PDF 2013
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Exploring Python
by
Timothy A. Budd
Exploring Python – Preface
1
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
5
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
3
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
4
(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
5
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
5
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
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