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Diffstat (limited to 'lib/python2.7/dumbdbm.py')
| -rw-r--r-- | lib/python2.7/dumbdbm.py | 250 |
1 files changed, 0 insertions, 250 deletions
diff --git a/lib/python2.7/dumbdbm.py b/lib/python2.7/dumbdbm.py deleted file mode 100644 index fb54a93..0000000 --- a/lib/python2.7/dumbdbm.py +++ /dev/null @@ -1,250 +0,0 @@ -"""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) |