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"""

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    Generic configuration file output

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"""

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import os, os.path, tempfile, shutil

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class ConfObject (object) :

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    """

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        An object that can be written to a ConfFile, as multiple lines of text.

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    """

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    def fmt_lines (self) :

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        """

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            Yield a series of lines to be output in the file

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        """

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        abstract

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class File (ConfObject) :

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    """

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        A single configuration file on the filesystem.

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        Configuration files are themselves ConfObject's, although this must be implemented in the inheriting class.

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    """

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    def __init__ (self, name, path, backup_suffix='.bak', mode=0644) :

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        """

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            Initialize the config file, but don't open it yet

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            @param name the human-readable friendly name for the config file

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            @param path the full filesystem path for the file

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            @param backup_suffix rename the old file by adding this suffix when replacing it

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            @param mode the permission bits for the new file

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        """

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        self.name = name

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        self.path = path

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        self.backup_suffix = backup_suffix

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        self.mode = mode

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    def write_file (self, file) :

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        """

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            Write out this config's stuff into the given file

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        """

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        writer = Writer(file)

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        writer.write_obj(self)

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    def write (self) :

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        """

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            Write out a new config file with this config's stuff using the following procedure:

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                * lock the real file

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                * open a new temporary file, and write out the objects into that, closing it

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                * move the real file out of the way

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                * move the temporary file into the real file's place

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                * unlock the real file

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        """

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        # XXX: how to aquire the lock?

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        # XXX: this needs checking over

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        # open the new temporary file

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        # XXX: ensure fd is closed

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        tmp_fd, tmp_path = tempfile.mkstemp(prefix=self.name)

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        # ...as a file

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        tmp_file = os.fdopen(tmp_fd, "w")

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        # fix the permissions

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        os.chmod(tmp_path, self.mode)

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        # write it

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        self.write_file(tmp_file)

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        # close it

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        tmp_file.close()

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        # move the old file out of the way

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        if os.path.exists(self.path) :

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            os.rename(self.path, self.path + self.backup_suffix)

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        # move the new file in

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        shutil.move(tmp_path, self.path)

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class Writer (object) :

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    """

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        A conf.Writer is used to write out a new conf.File (as a temporary file)

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    """

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    def __init__ (self, file) :

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        """

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            @param file the temporary file object

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        """

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        self.file = file

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    def write_line (self, line) :

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        """

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            Write a single line to the file

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        """

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        self.file.write("%s\n" % (line, ))

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    def write_lines (self, lines) :

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        """

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            Write a series of lines into the file

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        """

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        for line in lines :

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            self.write_line(line)

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    def write_obj (self, obj) :

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        """

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            Write a single object to the file

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        """

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        # just write out all the lines

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        self.write_lines(obj.fmt_lines())

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