保留注释换行的python模块configparser

python语言用来解析配置文件的模块是ConfigParser，python3中是configparser模块，我在使用中发现write方法在将配置项重新写入文

件时，配置文件中的空行和注释行都会被去掉，虽然这个并不影响使用，但配置文件的可读性无疑还是变差了，为此特地对ConfigParser模块进

行了一点改动，使其保留注释项和空行。

代码很简单。思路就是在读配置文件的时候碰到注释行或换行就缓存起来，然后在写入的时候从缓存中取出就可以了。

以python2为例，上代码：

1、修改 RawConfigParser 类定义，增加一个用于缓存注释行和空行的字典

class RawConfigParser:
    def __init__(self, defaults=None, dict_type=_default_dict,
                 allow_no_value=False):
        ... # 省略代码
        
        # comment or blank line temp cache
        self.comment_line_dict = {}

2、修改_read方法，缓存注释行和空行

    def _read(self, fp, fpname):
        """Parse a sectioned setup file.

        The sections in setup file contains a title line at the top,
        indicated by a name in square brackets (`[]'), plus key/value
        options lines, indicated by `name: value' format lines.
        Continuations are represented by an embedded newline then
        leading whitespace.  Blank lines, lines beginning with a '#',
        and just about everything else are ignored.
        """
        cursect = None                        # None, or a dictionary
        optname = None
        lineno = 0
        e = None                              # None, or an exception
        comment_line_cache = []               # comment or blank line temp cache
        while True:
            line = fp.readline()
            if not line:
                break
            lineno = lineno + 1
            # comment or blank line?
            if line.strip() == '' or line[0] in '#;':
                comment_line_cache.append(line.strip())
                continue
            if line.split(None, 1)[0].lower() == 'rem' and line[0] in "rR":
                # no leading whitespace
                comment_line_cache.append(line.strip())
                continue
            # continuation line?
            if line[0].isspace() and cursect is not None and optname:
                value = line.strip()
                if value:
                    cursect[optname].append(value)
            # a section header or option header?
            else:
                # is it a section header?
                mo = self.SECTCRE.match(line)
                if mo:
                    sectname = mo.group('header')
                    self.comment_line_dict[sectname] = comment_line_cache
                    comment_line_cache = []
                    if sectname in self._sections:
                        cursect = self._sections[sectname]
                    elif sectname == DEFAULTSECT:
                        cursect = self._defaults
                    else:
                        cursect = self._dict()
                        cursect['__name__'] = sectname
                        self._sections[sectname] = cursect
                    # So sections can't start with a continuation line
                    optname = None
                # no section header in the file?
                elif cursect is None:
                    raise MissingSectionHeaderError(fpname, lineno, line)
                # an option line?
                else:
                    mo = self._optcre.match(line)
                    if mo:
                        optname, vi, optval = mo.group('option', 'vi', 'value')
                        optname = self.optionxform(optname.rstrip())
                        self.comment_line_dict["%s.%s"%(cursect['__name__'], optname)] = comment_line_cache
                        comment_line_cache = []                        
                        # This check is fine because the OPTCRE cannot
                        # match if it would set optval to None
                        if optval is not None:
                            if vi in ('=', ':') and ';' in optval:
                                # ';' is a comment delimiter only if it follows
                                # a spacing character
                                pos = optval.find(';')
                                if pos != -1 and optval[pos-1].isspace():
                                    optval = optval[:pos]
                            optval = optval.strip()
                            # allow empty values
                            if optval == '""':
                                optval = ''
                            cursect[optname] = [optval]
                        else:
                            # valueless option handling
                            cursect[optname] = optval
                    else:
                        # a non-fatal parsing error occurred.  set up the
                        # exception but keep going. the exception will be
                        # raised at the end of the file and will contain a
                        # list of all bogus lines
                        if not e:
                            e = ParsingError(fpname)
                        e.append(lineno, repr(line))
        # if any parsing errors occurred, raise an exception
        if e:
            raise e

        # join the multi-line values collected while reading
        all_sections = [self._defaults]
        all_sections.extend(self._sections.values())
        for options in all_sections:
            for name, val in options.items():
                if isinstance(val, list):
                    options[name] = '
'.join(val)

 3、修改write方法，将保存的注释行和空行写入文件

    def write(self, fp):
        """Write an .ini-format representation of the configuration state."""
        if self._defaults:
            comment_line = self.comment_line_dict.get("%s"%(DEFAULTSECT), [])
            if comment_line:
                fp.write("
".join(comment_line) + "
")
            fp.write("[%s]
" % DEFAULTSECT)
            for (key, value) in self._defaults.items():
                comment_line = self.comment_line_dict.get("%s.%s"%(DEFAULTSECT, key), [])
                if comment_line:
                    fp.write("
".join(comment_line) + "
")
                fp.write("%s = %s
" % (key, str(value).replace('
', '
	')))
            fp.write("
")
        for section in self._sections:
            comment_line = self.comment_line_dict.get("%s"%(section), [])
            if comment_line:
                fp.write("
".join(comment_line) + "
")            
            fp.write("[%s]
" % section)
            for (key, value) in self._sections[section].items():
                if key == "__name__":
                    continue
                comment_line = self.comment_line_dict.get("%s.%s"%(section, key), [])
                if comment_line:
                    fp.write("
".join(comment_line) + "
")
                if (value is not None) or (self._optcre == self.OPTCRE):
                    key = " = ".join((key, str(value).replace('
', '
	')))
                fp.write("%s
" % (key))
            fp.write("
")

 完结。

python3和这个思路一样，只是代码结构有较大改动，这里就不粘贴代码了，想看的可以去这里:

https://github.com/duanyifei/configparser