TableOfContents

Python语言

1. Summary

Python is an interpreted programming language created by Guido van Rossum in 1990. Python is fully dynamically typed and uses automatic memory management; it is thus similar to Perl, Ruby, Scheme, Smalltalk, and Tcl. Python is developed as an open source project, managed by the non-profit Python Software Foundation, and is available for free from the project website. Python 2.4.3 was released on March 29, 2006.

注：In computer science, duck typing is a term for dynamic typing typical of some programming languages, such as Smalltalk or Visual FoxPro, where a variable's value itself determines what the variable can do. It also implies that an object is interchangeable with any other object that implements the same interface, regardless of whether the objects have a related inheritance hierarchy.

The term is a reference to the "duck test"—"If it walks like a duck and quacks like a duck, it must be a duck." One can also say that the duck typing method ducks the issue of typing variables.

Pythonic programming style that determines an object's type by inspection of its method or attribute signature rather than by explicit relationship to some type object ("If it looks like a duck and quacks like a duck, it must be a duck.") By emphasizing interfaces rather than specific types, well-designed code improves its flexibility by allowing polymorphic substitution. Duck-typing avoids tests using type() or isinstance(). Instead, it typically employs hasattr() tests or EAFP [Easier to Ask Forgiveness than Permission] programming.

The standard example of duck typing in Python is file-like classes. Classes can implement some or all of the methods of file and can be used where file would normally be used. For example, GzipFile implements a file-like object for accessing gzip-compressed data. cStringIO allows treating a Python string as a file. Sockets and files share many of the same methods as well. However, sockets lack the tell() method and cannot be used everywhere that GzipFile can be used. This shows the flexibility of duck typing: a file-like object can implement only methods it is able to, and consequently it can be only used in situations where it makes sense.

2. Philosophy

Python is a multi-paradigm language. This means that, rather than forcing coders to adopt one particular style of coding, it permits several. Object orientation, structured programming, functional programming, and aspect-oriented programming are all supported. Other paradigms can be supported through extensions, such as pyDBC and Contracts for Python which allow Design by Contract. Python is dynamically type-checked and uses garbage collection for memory management. An important feature of Python is dynamic name resolution, which binds method and variable names during program execution.

While offering choice in coding methodology, Python's designers reject exuberant syntax, such as in Perl, in favor of a sparser, less cluttered one. As with Perl, Python's developers expressly promote a particular "culture" or ideology based on what they want the language to be, favoring language forms they see as "beautiful", "explicit" and "simple". For the most part, Perl and Python users differ in their interpretation of these terms and how they are best implemented (see TIMTOWTDI and PythonPhilosophy).

Another important goal of the Python developers is making Python fun to use. This is reflected in the origin of the name (after the television series Monty Python's Flying Circus), in the common practice of using Monty Python references in example code, and in an occasionally playful approach to tutorials and reference materials. For example, the metasyntactic variables often used in Python literature are spam and eggs, instead of the traditional foo and bar.

Python is sometimes referred to as a "scripting language". In practice, it is used as a dynamic programming language for both application development and occasional scripting. Python has been used to develop many large software projects such as the Zope application server and the Mnet and BitTorrent file sharing systems. It is also extensively used by Google. [1]

Another important goal of the language is ease of extensibility. New built-in modules are easily written in C or C++. Python can also be used as an extension language for existing modules and applications that need a programmable interface.

Though the design of Python is somewhat hostile to functional programming (no tail call elimination or good support for anonymous closures) and the Lisp tradition, there are significant parallels between the philosophy of Python and that of minimalist Lisp-family languages such as Scheme. Many past Lisp programmers have found Python appealing for this reason.

3. Pythonic

A few neologisms have come into common use within the Python community. One of the most common is "pythonic", which can have a wide range of meanings related to program style. To say that a piece of code is pythonic is to say that it uses Python idioms well; that it is natural or shows fluency in the language. Likewise, to say of an interface or language feature that it is pythonic is to say that it works well with Python idioms; that its use meshes well with the rest of the language.

In contrast, a mark of unpythonic code is that it attempts to "write C++ (or Lisp, or Perl) code in Python"—that is, provides a rough transcription rather than an idiomatic translation of forms from another language.

The prefix Py- can be used to show that something is related to Python. Examples of the use of this prefix in names of Python applications or libraries include Pygame, a binding of SDL to Python (commonly used to create games), PyUI, a GUI encoded entirely in Python, and PySol, a series of solitaire card games programmed in Python.

Users and admirers of Python—most especially those considered knowledgeable or experienced—are often referred to as Pythonists, Pythonistas, and Pythoneers

4. Python的编码处理技术

对于中文用户，特别需要关注Python的编码技术. 列举一些常用的技巧。

chr(i): 将一个0到255的整数转换为一个字符.
ord(c): 返回单个字符c的整数顺序值.普通字符返回[0,255]中的一个值,Unicode字符返回 [0,65535]中的一个值
unichr(i): 将一个0到65535的整数转换为一个Unicode字符

• 代码中的编码设置，应该在代码最初两行内包含：

# -*- coding: UTF-8 -*-

• 获得/设置系统的缺省编码

sys.getdefaultencoding()

sys.setdefaultencoding('utf-8')

• 获得文件系统的文件名的编码

sys.getfilesystemencoding()

• 获得当前终端的输入、输出编码

      sys.stdout.encoding

      sys.stdin.encoding

• 编码转换（先转换为unicode，再转换为具体的编码），有两种方法：

      unicode('abc', 'mbcs').encode('utf-8')

      'abc'.decode('mbcs').encode('utf-8')

Python库

• 图像获取：linux平台下使用sane模块，Windows平台下使用twain模块

• 图像处理["PythonImageLibrary中文手册"]

• 使用_winreg模块操纵windows注册表
• 读取excel：用xlrd包。把excel转成csv，使用csv库操作。

• 将python程序打包成windows下可以执行的exe文件：使用[http://www.py2exe.org/ py2exe]模块

• 加密：Python Cryptography Toolkit http://www.amk.ca/python/code/crypto

• 在.net平台上使用python：[http://www.gotdotnet.com/Workspaces/Workspace.aspx?id=ad7acff7-ab1e-4bcb-99c0-57ac5a3a9742 IronPython]

学习资料

• [https://secure.wikimedia.org/wikipedia/zh/wiki/Python Wikipedia:Python]

• [http://diveintopython.org/ Dive Into Python]

• [http://www.woodpecker.org.cn/obp/diveintopython-zh-5.4/zh-cn/dist/html/toc/index.html dive into python最新中文版]

• [http://www.python.org/ Python官方站点]

• [http://python.cn/ Python中文社区]

• [http://groups.google.com/group/comp.lang.python Python讨论组comp.lang.python]

• [http://www.ibiblio.org/obp/thinkCSpy/ How to Think Like a Computer Scientist (Learning with Python)]

• [http://pine.fm/LearnToProgram/ Learn to Program(ruby)]

• [http://www-128.ibm.com/developerworks/cn/linux/theme/special/index.html#python]