.. _tut-intro:

**********************
Whetting Your Appetite
**********************

If you do much work on computers, eventually you find that there's some task
you'd like to automate.  For example, you may wish to perform a search-and-
replace over a large number of text files, or rename and rearrange a bunch of
photo files in a complicated way. Perhaps you'd like to write a small custom
database, or a specialized GUI application, or a simple game.

If you're a professional software developer, you may have to work with several
C/C++/Java libraries but find the usual write/compile/test/re-compile cycle is
too slow.  Perhaps you're writing a test suite for such a library and find
writing the testing code a tedious task.  Or maybe you've written a program that
could use an extension language, and you don't want to design and implement a
whole new language for your application.

Python is just the language for you.

You could write a Unix shell script or Windows batch files for some of these
tasks, but shell scripts are best at moving around files and changing text data,
not well-suited for GUI applications or games. You could write a C/C++/Java
program, but it can take a lot of development time to get even a first-draft
program.  Python is simpler to use, available on Windows, MacOS X, and Unix
operating systems, and will help you get the job done more quickly.

Python is simple to use, but it is a real programming language, offering much
more structure and support for large programs than shell scripts or batch files
can offer.  On the other hand, Python also offers much more error checking than
C, and, being a *very-high-level language*, it has high-level data types built
in, such as flexible arrays and dictionaries.  Because of its more general data
types Python is applicable to a much larger problem domain than Awk or even
Perl, yet many things are at least as easy in Python as in those languages.

Python allows you to split your program into modules that can be reused in other
Python programs.  It comes with a large collection of standard modules that you
can use as the basis of your programs --- or as examples to start learning to
program in Python.  Some of these modules provide things like file I/O, system
calls, sockets, and even interfaces to graphical user interface toolkits like
Tk.

Python is an interpreted language, which can save you considerable time during
program development because no compilation and linking is necessary.  The
interpreter can be used interactively, which makes it easy to experiment with
features of the language, to write throw-away programs, or to test functions
during bottom-up program development. It is also a handy desk calculator.

Python enables programs to be written compactly and readably.  Programs written
in Python are typically much shorter than equivalent C,  C++, or Java programs,
for several reasons:

* the high-level data types allow you to express complex operations in a single
  statement;

* statement grouping is done by indentation instead of beginning and ending
  brackets;

* no variable or argument declarations are necessary.

Python is *extensible*: if you know how to program in C it is easy to add a new
built-in function or module to the interpreter, either to perform critical
operations at maximum speed, or to link Python programs to libraries that may
only be available in binary form (such as a vendor-specific graphics library).
Once you are really hooked, you can link the Python interpreter into an
application written in C and use it as an extension or command language for that
application.

By the way, the language is named after the BBC show "Monty Python's Flying
Circus" and has nothing to do with nasty reptiles.  Making references to Monty
Python skits in documentation is not only allowed, it is encouraged!

Now that you are all excited about Python, you'll want to examine it in some
more detail.  Since the best way to learn a language is to use it, the tutorial
invites you to play with the Python interpreter as you read.

.. % \section{Where From Here \label{where}}

In the next chapter, the mechanics of using the interpreter are explained.  This
is rather mundane information, but essential for trying out the examples shown
later.

The rest of the tutorial introduces various features of the Python language and
system through examples, beginning with simple expressions, statements and data
types, through functions and modules, and finally touching upon advanced
concepts like exceptions and user-defined classes.


