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ΒΑ yαΎΓ "t """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.rena