python字符串转成列表

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