要让python文件支持UTF-8输入和显示，我们熟悉在文件第二行加入如下注释：

# -*- coding: <encoding name> -*-

但是为什么要这么写，到底写成什么格式是合法的，可以看下面这段说明：

Defining the Encoding        

Python will default to ASCII as standard encoding if no other encoding hints are given.

To define a source code encoding, a magic comment must be placed into the source files either as first or second line in the file, such as:

# coding=<encoding name>

or (using formats recognized by popular editors):

#!/usr/bin/python
# -*- coding: <encoding name> -*-

or:

#!/usr/bin/python
# vim: set fileencoding=<encoding name> :

More precisely, the first or second line must match the following regular expression:

^[ \t\v]*#.*?coding[:=][ \t]*([-_.a-zA-Z0-9]+)

The first group of this expression is then interpreted as encoding name. If the encoding is unknown to Python, an error is raised during compilation. There must not be any Python statement on the line that contains the encoding declaration.  If the first line matches the second line is ignored.

To aid with platforms such as Windows, which add Unicode BOM marks to the beginning of Unicode files, the UTF-8 signature         \xef\xbb\xbf        will be interpreted as ‘utf-8‘ encoding as well (even if no magic encoding comment is given).

If a source file uses both the UTF-8 BOM mark signature and a magic encoding comment, the only allowed encoding for the comment is ‘utf-8‘.  Any other encoding will cause an error. 

所以，只要在文件第一行或者第二行，满足如下正则表达式，均是合法的指定编码方式的方法：

^[ \t\v]*#.*?coding[:=][ \t]*([-_.a-zA-Z0-9]+)

那么为什么一般都写成

# -*- coding: <encoding name> -*-

呢？原来这是Emacs编辑器的风格，其实也可以使用其它风格，比如：

These are some examples to clarify the different styles for defining the source code encoding at the top of a Python source file:

1. With interpreter binary and using Emacs style file encoding comment:

   #!/usr/bin/python
   # -*- coding: latin-1 -*-
   import os, sys
   ...
   
   #!/usr/bin/python
   # -*- coding: iso-8859-15 -*-
   import os, sys
   ...
   
   #!/usr/bin/python
   # -*- coding: ascii -*-
   import os, sys
   ...

2. Without interpreter line, using plain text:

   # This Python file uses the following encoding: utf-8
   import os, sys
   ...

3. Text editors might have different ways of defining the file‘s encoding, e.g.:

   #!/usr/local/bin/python
   # coding: latin-1
   import os, sys
   ...

所以并不是必须要写成这种风格，只是一种约定俗成罢了。

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