| """A dumb and slow but simple dbm clone. | |
| For database spam, spam.dir contains the index (a text file), | |
| spam.bak *may* contain a backup of the index (also a text file), | |
| while spam.dat contains the data (a binary file). | |
| XXX TO DO: | |
| - seems to contain a bug when updating... | |
| - reclaim free space (currently, space once occupied by deleted or expanded | |
| items is never reused) | |
| - support concurrent access (currently, if two processes take turns making | |
| updates, they can mess up the index) | |
| - support efficient access to large databases (currently, the whole index | |
| is read when the database is opened, and some updates rewrite the whole index) | |
| - support opening for read-only (flag = 'm') | |
| """ | |
| import os as _os | |
| import __builtin__ | |
| import UserDict | |
| _open = __builtin__.open | |
| _BLOCKSIZE = 512 | |
| error = IOError # For anydbm | |
| class _Database(UserDict.DictMixin): | |
| # The on-disk directory and data files can remain in mutually | |
| # inconsistent states for an arbitrarily long time (see comments | |
| # at the end of __setitem__). This is only repaired when _commit() | |
| # gets called. One place _commit() gets called is from __del__(), | |
| # and if that occurs at program shutdown time, module globals may | |
| # already have gotten rebound to None. Since it's crucial that | |
| # _commit() finish successfully, we can't ignore shutdown races | |
| # here, and _commit() must not reference any globals. | |
| _os = _os # for _commit() | |
| _open = _open # for _commit() | |
| def __init__(self, filebasename, mode): | |
| self._mode = mode | |
| # The directory file is a text file. Each line looks like | |
| # "%r, (%d, %d)\n" % (key, pos, siz) | |
| # where key is the string key, pos is the offset into the dat | |
| # file of the associated value's first byte, and siz is the number | |
| # of bytes in the associated value. | |
| self._dirfile = filebasename + _os.extsep + 'dir' | |
| # The data file is a binary file pointed into by the directory | |
| # file, and holds the values associated with keys. Each value | |
| # begins at a _BLOCKSIZE-aligned byte offset, and is a raw | |
| # binary 8-bit string value. | |
| self._datfile = filebasename + _os.extsep + 'dat' | |
| self._bakfile = filebasename + _os.extsep + 'bak' | |
| # The index is an in-memory dict, mirroring the directory file. | |
| self._index = None # maps keys to (pos, siz) pairs | |
| # Mod by Jack: create data file if needed | |
| try: | |
| f = _open(self._datfile, 'r') | |
| except IOError: | |
| f = _open(self._datfile, 'w') | |
| self._chmod(self._datfile) | |
| f.close() | |
| self._update() | |
| # Read directory file into the in-memory index dict. | |
| def _update(self): | |
| self._index = {} | |
| try: | |
| f = _open(self._dirfile) | |
| except IOError: | |
| pass | |
| else: | |
| for line in f: | |
| line = line.rstrip() | |
| key, pos_and_siz_pair = eval(line) | |
| self._index[key] = pos_and_siz_pair | |
| f.close() | |
| # Write the index dict to the directory file. The original directory | |
| # file (if any) is renamed with a .bak extension first. If a .bak | |
| # file currently exists, it's deleted. | |
| def _commit(self): | |
| # CAUTION: It's vital that _commit() succeed, and _commit() can | |
| # be called from __del__(). Therefore we must never reference a | |
| # global in this routine. | |
| if self._index is None: | |
| return # nothing to do | |
| try: | |
| self._os.unlink(self._bakfile) | |
| except self._os.error: | |
| pass | |
| try: | |
| self._os.rename(self._dirfile, self._bakfile) | |
| except self._os.error: | |
| pass | |
| f = self._open(self._dirfile, 'w') | |
| self._chmod(self._dirfile) | |
| for key, pos_and_siz_pair in self._index.iteritems(): | |
| f.write("%r, %r\n" % (key, pos_and_siz_pair)) | |
| f.close() | |
| sync = _commit | |
| def __getitem__(self, key): | |
| pos, siz = self._index[key] # may raise KeyError | |
| f = _open(self._datfile, 'rb') | |
| f.seek(pos) | |
| dat = f.read(siz) | |
| f.close() | |
| return dat | |
| # Append val to the data file, starting at a _BLOCKSIZE-aligned | |
| # offset. The data file is first padded with NUL bytes (if needed) | |
| # to get to an aligned offset. Return pair | |
| # (starting offset of val, len(val)) | |
| def _addval(self, val): | |
| f = _open(self._datfile, 'rb+') | |
| f.seek(0, 2) | |
| pos = int(f.tell()) | |
| npos = ((pos + _BLOCKSIZE - 1) // _BLOCKSIZE) * _BLOCKSIZE | |
| f.write('\0'*(npos-pos)) | |
| pos = npos | |
| f.write(val) | |
| f.close() | |
| return (pos, len(val)) | |
| # Write val to the data file, starting at offset pos. The caller | |
| # is responsible for ensuring that there's enough room starting at | |
| # pos to hold val, without overwriting some other value. Return | |
| # pair (pos, len(val)). | |
| def _setval(self, pos, val): | |
| f = _open(self._datfile, 'rb+') | |
| f.seek(pos) | |
| f.write(val) | |
| f.close() | |
| return (pos, len(val)) | |
| # key is a new key whose associated value starts in the data file | |
| # at offset pos and with length siz. Add an index record to | |
| # the in-memory index dict, and append one to the directory file. | |
| def _addkey(self, key, pos_and_siz_pair): | |
| self._index[key] = pos_and_siz_pair | |
| f = _open(self._dirfile, 'a') | |
| self._chmod(self._dirfile) | |
| f.write("%r, %r\n" % (key, pos_and_siz_pair)) | |
| f.close() | |
| def __setitem__(self, key, val): | |
| if not type(key) == type('') == type(val): | |
| raise TypeError, "keys and values must be strings" | |
| if key not in self._index: | |
| self._addkey(key, self._addval(val)) | |
| else: | |
| # See whether the new value is small enough to fit in the | |
| # (padded) space currently occupied by the old value. | |
| pos, siz = self._index[key] | |
| oldblocks = (siz + _BLOCKSIZE - 1) // _BLOCKSIZE | |
| newblocks = (len(val) + _BLOCKSIZE - 1) // _BLOCKSIZE | |
| if newblocks <= oldblocks: | |
| self._index[key] = self._setval(pos, val) | |
| else: | |
| # The new value doesn't fit in the (padded) space used | |
| # by the old value. The blocks used by the old value are | |
| # forever lost. | |
| self._index[key] = self._addval(val) | |
| # Note that _index may be out of synch with the directory | |
| # file now: _setval() and _addval() don't update the directory | |
| # file. This also means that the on-disk directory and data | |
| # files are in a mutually inconsistent state, and they'll | |
| # remain that way until _commit() is called. Note that this | |
| # is a disaster (for the database) if the program crashes | |
| # (so that _commit() never gets called). | |
| def __delitem__(self, key): | |
| # The blocks used by the associated value are lost. | |
| del self._index[key] | |
| # XXX It's unclear why we do a _commit() here (the code always | |
| # XXX has, so I'm not changing it). _setitem__ doesn't try to | |
| # XXX keep the directory file in synch. Why should we? Or | |
| # XXX why shouldn't __setitem__? | |
| self._commit() | |
| def keys(self): | |
| return self._index.keys() | |
| def has_key(self, key): | |
| return key in self._index | |
| def __contains__(self, key): | |
| return key in self._index | |
| def iterkeys(self): | |
| return self._index.iterkeys() | |
| __iter__ = iterkeys | |
| def __len__(self): | |
| return len(self._index) | |
| def close(self): | |
| self._commit() | |
| self._index = self._datfile = self._dirfile = self._bakfile = None | |
| __del__ = close | |
| def _chmod (self, file): | |
| if hasattr(self._os, 'chmod'): | |
| self._os.chmod(file, self._mode) | |
| def open(file, flag=None, mode=0666): | |
| """Open the database file, filename, and return corresponding object. | |
| The flag argument, used to control how the database is opened in the | |
| other DBM implementations, is ignored in the dumbdbm module; the | |
| database is always opened for update, and will be created if it does | |
| not exist. | |
| The optional mode argument is the UNIX mode of the file, used only when | |
| the database has to be created. It defaults to octal code 0666 (and | |
| will be modified by the prevailing umask). | |
| """ | |
| # flag argument is currently ignored | |
| # Modify mode depending on the umask | |
| try: | |
| um = _os.umask(0) | |
| _os.umask(um) | |
| except AttributeError: | |
| pass | |
| else: | |
| # Turn off any bits that are set in the umask | |
| mode = mode & (~um) | |
| return _Database(file, mode) |