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- """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')
-
- """
-
- _os = __import__('os')
- import __builtin__
-
- _open = __builtin__.open
-
- _BLOCKSIZE = 512
-
- error = IOError # For anydbm
-
- class _Database:
-
- def __init__(self, file):
- self._dirfile = file + '.dir'
- self._datfile = file + '.dat'
- self._bakfile = file + '.bak'
- # Mod by Jack: create data file if needed
- try:
- f = _open(self._datfile, 'r')
- except IOError:
- f = _open(self._datfile, 'w')
- f.close()
- self._update()
-
- def _update(self):
- self._index = {}
- try:
- f = _open(self._dirfile)
- except IOError:
- pass
- else:
- while 1:
- line = f.readline()
- if not line: break
- key, (pos, siz) = eval(line)
- self._index[key] = (pos, siz)
- f.close()
-
- def _commit(self):
- try: _os.unlink(self._bakfile)
- except _os.error: pass
- try: _os.rename(self._dirfile, self._bakfile)
- except _os.error: pass
- f = _open(self._dirfile, 'w')
- for key, (pos, siz) in self._index.items():
- f.write("%s, (%s, %s)\n" % (`key`, `pos`, `siz`))
- f.close()
-
- 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
-
- def _addval(self, val):
- f = _open(self._datfile, 'rb+')
- f.seek(0, 2)
- pos = f.tell()
- ## Does not work under MW compiler
- ## pos = ((pos + _BLOCKSIZE - 1) / _BLOCKSIZE) * _BLOCKSIZE
- ## f.seek(pos)
- npos = ((pos + _BLOCKSIZE - 1) / _BLOCKSIZE) * _BLOCKSIZE
- f.write('\0'*(npos-pos))
- pos = npos
-
- f.write(val)
- f.close()
- return (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))
-
- def _addkey(self, key, (pos, siz)):
- self._index[key] = (pos, siz)
- f = _open(self._dirfile, 'a')
- f.write("%s, (%s, %s)\n" % (`key`, `pos`, `siz`))
- f.close()
-
- def __setitem__(self, key, val):
- if not type(key) == type('') == type(val):
- raise TypeError, "keys and values must be strings"
- if not self._index.has_key(key):
- (pos, siz) = self._addval(val)
- self._addkey(key, (pos, siz))
- else:
- pos, siz = self._index[key]
- oldblocks = (siz + _BLOCKSIZE - 1) / _BLOCKSIZE
- newblocks = (len(val) + _BLOCKSIZE - 1) / _BLOCKSIZE
- if newblocks <= oldblocks:
- pos, siz = self._setval(pos, val)
- self._index[key] = pos, siz
- else:
- pos, siz = self._addval(val)
- self._index[key] = pos, siz
- self._addkey(key, (pos, siz))
-
- def __delitem__(self, key):
- del self._index[key]
- self._commit()
-
- def keys(self):
- return self._index.keys()
-
- def has_key(self, key):
- return self._index.has_key(key)
-
- def __len__(self):
- return len(self._index)
-
- def close(self):
- self._index = None
- self._datfile = self._dirfile = self._bakfile = None
-
-
- def open(file, flag = None, mode = None):
- # flag, mode arguments are currently ignored
- return _Database(file)
-