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17 | <title>1. Whetting Your Appetite </title> | |
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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> | |
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191 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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