Python入门指南：简洁高效的语言与开发工具

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本篇文档是Python的入门指南，由Guido van Rossum编写，发布于2006年7月11日，由Python Software Foundation发行。Python被设计为一种易学且功能强大的编程语言，特别适合初学者。它拥有高效的数据结构和简洁的对象导向编程方式。Python的语法优雅，动态类型以及解释执行特性使其在脚本编写和快速应用开发中表现出色，能够在多个平台上运行。文档强调了Python的简洁性，如其富有表达力的语法，这使得代码易于阅读和理解。Python的动态类型系统允许开发者在运行时决定变量的类型，降低了类型错误的可能性，提高了开发效率。此外，它的可扩展性体现在标准库的广泛可用性上，无论是源码还是二进制形式，Python的解释器和标准库都是免费提供给所有主要平台的。然而，文档也提示读者在阅读过程中需留意可能存在的错误或不准确之处，暗示着学习者需要具备一定的细心和批判性思维，以充分利用这份资源。这是一份既适合新手入门，又包含深入内容的Python教程，提供了丰富的基础知识，同时也对高级编程概念有所涉及。通过学习这份指南，读者可以逐步掌握Python的基本语法、数据结构、面向对象编程、模块和库的使用，以及如何利用Python进行高效的开发工作。

exception, which may be handled by a try statement.

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2.2.2 Executable Python Scripts 1Python

On BSD’ish UNIX systems, Python scripts can be made directly executable, like shell scripts, by putting the line

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#! /usr/bin/env python

(assuming that the interpreter is on the user’s PATH) at the beginning of the script and giving the ﬁle an executable

mode. The ‘#!’ must be the ﬁrst two characters of the ﬁle. On some platforms, this ﬁrst line must end with a

UNIX-style line ending (‘\n’), not a Mac OS (‘\r’) or Windows (‘\r\n’) line ending. Note that the hash, or pound,

character, ‘#’, is used to start a comment in Python.

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The script can be given an executable mode, or permission, using the chmod command:

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$ chmod +x myscript.py

2.2.3 Source Code Encoding §S?è

It is possible to use encodings different than ASCII in Python source ﬁles. The best way to do it is to put one more

special comment line right after the #! line to deﬁne the source ﬁle encoding:

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# -

- coding: encoding -

With that declaration, all characters in the source ﬁle will be treated as having the encoding encoding, and it will be

possible to directly write Unicode string literals in the selected encoding. The list of possible encodings can be found

in the Python Library Reference, in the section on codecs.

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For example, to write Unicode literals including the Euro currency symbol, the ISO-8859-15 encoding can be used,

with the Euro symbol having the ordinal value 164. This script will print the value 8364 (the Unicode codepoint

corresponding to the Euro symbol) and then exit:

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8 Chapter 2. Using the Python Interpreter ¦^Python)ºì

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# -

- coding: iso-8859-15 -

currency = u"C"

print ord(currency)

If your editor supports saving ﬁles as UTF-8 with a UTF-8 byte order mark (aka BOM), you can use that in-

stead of an encoding declaration. IDLE supports this capability if Options/General/Default Source

Encoding/UTF-8 is set. Notice that this signature is not understood in older Python releases (2.2 and earlier),

and also not understood by the operating system for script ﬁles with #! lines (only used on UNIX systems).

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ù5O?è(²"IDLE±ÏL½Options/General/Default Source Encoding/UTF-8 5

|±§"I5¿´ÎPythonØ|±ùIP£Python 2.2½@ ¤§Ó|±#!1öX Ú

Ø¬|±§£=^uUNIXXÚ¤"

By using UTF-8 (either through the signature or an encoding declaration), characters of most languages in the world

can be used simultaneously in string literals and comments. Using non-ASCII characters in identiﬁers is not supported.

To display all these characters properly, your editor must recognize that the ﬁle is UTF-8, and it must use a font that

supports all the characters in the ﬁle.

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When you use Python interactively, it is frequently handy to have some standard commands executed every time the

interpreter is started. You can do this by setting an environment variable named PYTHONSTARTUP to the name of a

ﬁle containing your start-up commands. This is similar to the ‘.proﬁle’ feature of the UNIX shells.

This ﬁle is only read in interactive sessions, not when Python reads commands from a script, and not when ‘/dev/tty’

is given as the explicit source of commands (which otherwise behaves like an interactive session). It is executed in

the same namespace where interactive commands are executed, so that objects that it deﬁnes or imports can be used

without qualiﬁcation in the interactive session. You can also change the prompts sys.ps1 and sys.ps2 in this ﬁle.

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If you want to read an additional start-up ﬁle from the current directory, you can program this in the global start-

up ﬁle using code like ‘if os.path.isfile(’.pythonrc.py’): execfile(’.pythonrc.py’)’. If

you want to use the startup ﬁle in a script, you must do this explicitly in the script:

os.path.isfile(’.pythonrc.py’): execfile(’.pythonrc.py’)’"XJ\3,¥

2.2. The Interpreter and Its Environment )ºì9Ù¸ 9

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