第819页 | Learning Python | 阅读 ‧ 电子书库

Source File Character Set Encoding Declarations

Unicode escape codes are fine for the occasional Unicode character in string literals, but they can become tedious if you need to embed non-ASCII text in your strings frequently. For strings you code within your script files, Python uses the UTF-8 encoding by default, but it allows you to change this to support arbitrary character sets by including a comment that names your desired encoding. The comment must be of this form and must appear as either the first or second line in your script in either Python 2.6 or 3.0:

# -*- coding: latin-1 -*-

When a comment of this form is present, Python will recognize strings represented natively in the given encoding. This means you can edit your script file in a text editor that accepts and displays accented and other non-ASCII characters correctly, and Python will decode them correctly in your string literals. For example, notice how the comment at the top of the following file, text.py, allows Latin-1 characters to be embedded in strings:

# -*- coding: latin-1 -*-

# Any of the following string literal forms work in latin-1.
# Changing the encoding above to either ascii or utf-8 fails,
# because the 0xc4 and 0xe8 in myStr1 are not valid in either.

myStr1 = 'aÄBèC'

myStr2 = 'A\u00c4B\U000000e8C'

myStr3 = 'A' + chr(0xC4) + 'B' + chr(0xE8) + 'C'

import sys
print('Default encoding:', sys.getdefaultencoding())

for aStr in myStr1, myStr2, myStr3:
    print('{0}, strlen={1}, '.format(aStr, len(aStr)), end='')

    bytes1 = aStr.encode()              # Per default utf-8: 2 bytes for non-ASCII
    bytes2 = aStr.encode('latin-1')     # One byte per char
   #bytes3 = aStr.encode('ascii')       # ASCII fails: outside 0..127 range

    print('byteslen1={0}, byteslen2={1}'.format(len(bytes1), len(bytes2)))

When run, this script produces the following output:

C:\misc> c:\python30\python text.py
Default encoding: utf-8
aÄBèC, strlen=5, byteslen1=7, byteslen2=5
AÄBèC, strlen=5, byteslen1=7, byteslen2=5
AÄBèC, strlen=5, byteslen1=7, byteslen2=5

Since most programmers are likely to fall back on the standard UTF-8 encoding, I’ll defer to Python’s standard manual set for more details on this option and other advanced Unicode support topics, such as properties and character name escapes in strings.