1 _orig_open = open

     2 

     3 class _BkFile:

     4     def __init__(self, file, mode, bufsize):

     5         import os

     6         self.__filename = file

     7         self.__backup = file + '~'

     8         try:

     9             os.unlink(self.__backup)

    10         except os.error:

    11             pass

    12         try:

    13             os.rename(file, self.__backup)

    14         except os.error:

    15             self.__backup = None

    16         self.__file = _orig_open(file, mode, bufsize)

    17         self.closed = self.__file.closed

    18         self.fileno = self.__file.fileno

    19         self.flush = self.__file.flush

    20         self.isatty = self.__file.isatty

    21         self.mode = self.__file.mode

    22         self.name = self.__file.name

    23         self.read = self.__file.read

    24         self.readinto = self.__file.readinto

    25         self.readline = self.__file.readline

    26         self.readlines = self.__file.readlines

    27         self.seek = self.__file.seek

    28         self.softspace = self.__file.softspace

    29         self.tell = self.__file.tell

    30         self.truncate = self.__file.truncate

    31         self.write = self.__file.write

    32         self.writelines = self.__file.writelines

    33 

    34     def close(self):

    35         self.__file.close()

    36         if self.__backup is None:

    37             return

    38         import filecmp

    39         if filecmp.cmp(self.__backup, self.__filename, shallow = 0):

    40             import os

    41             os.unlink(self.__filename)

    42             os.rename(self.__backup, self.__filename)

    43 

    44 def open(file, mode = 'r', bufsize = -1):

    45     if 'w' not in mode:

    46         return _orig_open(file, mode, bufsize)

    47     return _BkFile(file, mode, bufsize)