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<H1><A NAME="SECTION003000000000000000000"></A><A NAME="intro"></A>
<BR>
1. Whetting Your Appetite 
</H1>

<P>
If you ever wrote a large shell script, you probably know this
feeling: you'd love to add yet another feature, but it's already so
slow, and so big, and so complicated; or the feature involves a system
call or other function that is only accessible from C ...Usually
the problem at hand isn't serious enough to warrant rewriting the
script in C; perhaps the problem requires variable-length strings or
other data types (like sorted lists of file names) that are easy in
the shell but lots of work to implement in C, or perhaps you're not
sufficiently familiar with C.

<P>
Another situation: perhaps you have to work with several C libraries,
and the usual C write/compile/test/re-compile cycle is too slow.  You
need to develop software more quickly.  Possibly you've
written a program that could use an extension language, and you don't
want to design a language, write and debug an interpreter for it, then
tie it into your application.

<P>
In such cases, Python may be just the language for you.  Python is
simple to use, but it is a real programming language, offering much
more structure and support for large programs than the shell has.  On
the other hand, it also offers much more error checking than C, and,
being a <em>very-high-level language</em>, it has high-level data types
built in, such as flexible arrays and dictionaries that would cost you
days to implement efficiently in C.  Because of its more general data
types Python is applicable to a much larger problem domain than
<em>Awk</em> or even <em>Perl</em>, yet many things are at least as easy
in Python as in those languages.

<P>
Python allows you to split your program in 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.  

<P>
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.

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

<UL>
<LI>the high-level data types allow you to express complex operations in a
single statement;
</LI>
<LI>statement grouping is done by indentation instead of beginning and ending
brackets;
</LI>
<LI>no variable or argument declarations are necessary.
</LI>
</UL>

<P>
Python is <em>extensible</em>: 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.

<P>
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!

<P>
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, you are invited to do so with this tutorial.

<P>
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.

<P>
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.

<P>

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920dae64 AT	1	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
	2	<html>
	3	<head>
	4	<link rel="STYLESHEET" href="tut.css" type='text/css' />
	5	<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
	6	<link rel='start' href='../index.html' title='Python Documentation Index' />
	7	<link rel="first" href="tut.html" title='Python Tutorial' />
	8	<link rel='contents' href='node2.html' title="Contents" />
	9	<link rel='index' href='node19.html' title='Index' />
	10	<link rel='last' href='about.html' title='About this document...' />
	11	<link rel='help' href='about.html' title='About this document...' />
	12	<link rel="next" href="node4.html" />
	13	<link rel="prev" href="node2.html" />
	14	<link rel="parent" href="tut.html" />
	15	<link rel="next" href="node4.html" />
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	18	</head>
	19	<body>
	20	<DIV CLASS="navigation">
	21	<div id='top-navigation-panel' xml:id='top-navigation-panel'>
	22	<table align="center" width="100%" cellpadding="0" cellspacing="2">
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	25	href="node2.html"><img src='../icons/previous.png'
	26	border='0' height='32' alt='Previous Page' width='32' /></A></td>
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	36	border='0' height='32' alt='Contents' width='32' /></A></td>
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	54
	55	<H1><A NAME="SECTION003000000000000000000"></A><A NAME="intro"></A>
	56	<BR>
	57	1. Whetting Your Appetite
	58	</H1>
	59
	60	<P>
	61	If you ever wrote a large shell script, you probably know this
	62	feeling: you'd love to add yet another feature, but it's already so
	63	slow, and so big, and so complicated; or the feature involves a system
	64	call or other function that is only accessible from C ...Usually
65	the problem at hand isn't serious enough to warrant rewriting the
66	script in C; perhaps the problem requires variable-length strings or
67	other data types (like sorted lists of file names) that are easy in
68	the shell but lots of work to implement in C, or perhaps you're not
69	sufficiently familiar with C.
70
71	<P>
72	Another situation: perhaps you have to work with several C libraries,
73	and the usual C write/compile/test/re-compile cycle is too slow. You
74	need to develop software more quickly. Possibly you've
75	written a program that could use an extension language, and you don't
76	want to design a language, write and debug an interpreter for it, then
77	tie it into your application.
78
79	<P>
80	In such cases, Python may be just the language for you. Python is
81	simple to use, but it is a real programming language, offering much
82	more structure and support for large programs than the shell has. On
83	the other hand, it also offers much more error checking than C, and,
84	being a <em>very-high-level language</em>, it has high-level data types
85	built in, such as flexible arrays and dictionaries that would cost you
86	days to implement efficiently in C. Because of its more general data
87	types Python is applicable to a much larger problem domain than
88	<em>Awk</em> or even <em>Perl</em>, yet many things are at least as easy
89	in Python as in those languages.
90
91	<P>
92	Python allows you to split your program in modules that can be
93	reused in other Python programs. It comes with a large collection of
94	standard modules that you can use as the basis of your programs -- or
95	as examples to start learning to program in Python. Some of these
96	modules provide things like file I/O, system calls,
97	sockets, and even interfaces to graphical user interface toolkits like Tk.
98
99	<P>
100	Python is an interpreted language, which can save you considerable time
101	during program development because no compilation and linking is
102	necessary. The interpreter can be used interactively, which makes it
103	easy to experiment with features of the language, to write throw-away
104	programs, or to test functions during bottom-up program development.
105	It is also a handy desk calculator.
106
107	<P>
108	Python enables programs to written compactly and readably. Programs
109	written in Python are typically much shorter than equivalent C or
110	C++ programs, for several reasons:
111
112	<UL>
113	<LI>the high-level data types allow you to express complex operations in a
114	single statement;
115	</LI>
116	<LI>statement grouping is done by indentation instead of beginning and ending
117	brackets;
118	</LI>
119	<LI>no variable or argument declarations are necessary.
120	</LI>
121	</UL>
122
123	<P>
124	Python is <em>extensible</em>: if you know how to program in C it is easy
125	to add a new built-in function or module to the interpreter, either to
126	perform critical operations at maximum speed, or to link Python
127	programs to libraries that may only be available in binary form (such
128	as a vendor-specific graphics library). Once you are really hooked,
129	you can link the Python interpreter into an application written in C
130	and use it as an extension or command language for that application.
131
132	<P>
133	By the way, the language is named after the BBC show ``Monty Python's
134	Flying Circus'' and has nothing to do with nasty reptiles. Making
135	references to Monty Python skits in documentation is not only allowed,
136	it is encouraged!
137
138	<P>
139	Now that you are all excited about Python, you'll want to examine it
140	in some more detail. Since the best way to learn a language is
141	to use it, you are invited to do so with this tutorial.
142
143	<P>
144	In the next chapter, the mechanics of using the interpreter are
145	explained. This is rather mundane information, but essential for
146	trying out the examples shown later.
147
148	<P>
149	The rest of the tutorial introduces various features of the Python
150	language and system through examples, beginning with simple
151	expressions, statements and data types, through functions and modules,
152	and finally touching upon advanced concepts like exceptions
153	and user-defined classes.
154
155	<P>
156
157	<DIV CLASS="navigation">
158	<div class='online-navigation'>
159	<p></p><hr />
160	<table align="center" width="100%" cellpadding="0" cellspacing="2">
161	<tr>
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163	href="node2.html"><img src='../icons/previous.png'
164	border='0' height='32' alt='Previous Page' width='32' /></A></td>
165	<td class='online-navigation'><a rel="parent" title="Python Tutorial"
166	href="tut.html"><img src='../icons/up.png'
167	border='0' height='32' alt='Up One Level' width='32' /></A></td>
168	<td class='online-navigation'><a rel="next" title="2. Using the Python"
169	href="node4.html"><img src='../icons/next.png'
170	border='0' height='32' alt='Next Page' width='32' /></A></td>
171	<td align="center" width="100%">Python Tutorial</td>
172	<td class='online-navigation'><a rel="contents" title="Table of Contents"
173	href="node2.html"><img src='../icons/contents.png'
174	border='0' height='32' alt='Contents' width='32' /></A></td>
175	<td class='online-navigation'><img src='../icons/blank.png'
176	border='0' height='32' alt='' width='32' /></td>
177	<td class='online-navigation'><a rel="index" title="Index"
178	href="node19.html"><img src='../icons/index.png'
179	border='0' height='32' alt='Index' width='32' /></A></td>
180	</tr></table>
181	<div class='online-navigation'>
182	<b class="navlabel">Previous:</b>
183	<a class="sectref" rel="prev" href="node2.html">Contents</A>
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186	<b class="navlabel">Next:</b>
187	<a class="sectref" rel="next" href="node4.html">2. Using the Python</A>
188	</div>
189	</div>
190	<hr />
191	<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
192	</DIV>
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