Python编程中对于头部注释的要求

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.

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
   ...
   

4. Without encoding comment, Python's parser will assume ASCII text:

   #!/usr/local/bin/python
   import os, sys
   ...
   

5. Encoding comments which don't work:

   1. Missing "coding:" prefix:

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

   2. Encoding comment not on line 1 or 2:

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

   3. Unsupported encoding:

      #!/usr/local/bin/python
      # -*- coding: utf-42 -*-
      import os, sys
      ...