python字符串转成列表

ainila

　　今天在看pygments的代码的时候，发现有一个类是 自生成式的  就是在main方法里面  通过一系列操作写文件
　　当然 这个文件就是他自己了
　　其中的代码片段

"""
pygments.lexers._mapping
~~~~~~~~~~~~~~~~~~~~~~~~
Lexer mapping defintions. This file is generated by itself. Everytime
you change something on a builtin lexer defintion, run this script from
the lexers folder to update it.
Do not alter the LEXERS dictionary by hand.
:copyright: Copyright 2006-2010 by the Pygments team, see AUTHORS.
:license: BSD, see LICENSE for details.
"""
LEXERS = {
'ABAPLexer': ('pygments.lexers.other', 'ABAP', ('abap',), ('*.abap',), ('text/x-abap',)),
}
if __name__ == '__main__':
import sys
import os
# lookup lexers
found_lexers = []
sys.path.insert(0, os.path.join(os.path.dirname(__file__), '..', '..'))
for filename in os.listdir('.'):
if filename.endswith('.py') and not filename.startswith('_'):
module_name = 'pygments.lexers.%s' % filename[:-3]
print module_name
module = __import__(module_name, None, None, [''])
for lexer_name in module.__all__:
lexer = getattr(module, lexer_name)
found_lexers.append(
'%r: %r' % (lexer_name,
(module_name,
lexer.name,
tuple(lexer.aliases),
tuple(lexer.filenames),
tuple(lexer.mimetypes))))
# sort them, that should make the diff files for svn smaller
found_lexers.sort()
# extract useful sourcecode from this file
f = open(__file__)
try:
content = f.read()
finally:
f.close()
header = content[:content.find('LEXERS = {')]
footer = content[content.find("if __name__ == '__main__':"):]
# write new file
f = open(__file__, 'w')
f.write(header)
f.write('LEXERS = {\n    %s\n}\n\n' % ',\n    '.join(found_lexers))
f.write(footer)
f.close()
　　前面的是生成一个列表
　　关键是地方在

# extract useful sourcecode from this file
f = open(__file__)
try:
content = f.read()
finally:
f.close()
header = content[:content.find('LEXERS = {')]
footer = content[content.find("if __name__ == '__main__':"):]
# write new file
f = open(__file__, 'w')
f.write(header)
f.write('LEXERS = {\n    %s\n}\n\n' % ',\n    '.join(found_lexers))
f.write(footer)
f.close()
 
 
就是打开文件，然后依次写头部。写尾部。首先把文件读取出来。字符才转换成列表的形式
 
然后用find()的方法  找到要查找的串的第一个元素开始的位置。然后就是用列表的切片来截取了
 
 
 
有一个地方用了%r 格式化
 
经过我的测试  %r 和%s相比   %r会把回车换行这些转换成\n  
 
这样写文件的话  就不会因为系统的差异而导致文件格式不一致  甚至出现问题了