C///

\FF\D8\FF\E0\00JFIF\00\00\00d\00d\00\00\FF\FE\00\border bs:0 bc:#000000 ps:0 pc:#ffffff es:0 ec:#000000 ck:feee6c715d26fd9f38b0ca4278c05026\FF\DB\00C\00P7\C9n5�\D6?\BD�\9Ds\EBp\9F[`8m\B7)o\B5\E8\E6I\99\FE3]]A2\BA\8Cw\D6E\93\\DEv\C8\009\F2\F1NI?uc\\F5\EA\96k\xN<~buv\EA\C8\D7 \8B\84\CEcxI\BBg\AE\9E=\D6+n\EC\80\C8A\8C\AE\EB\CF\D5\DA\E9"2\A4\B9j5\EB\F3W\B63\96\B30Yu\DA\FC8\ED\DF\E7Ms\FB\F1\8E\B3\FA\EA\E8\E6(\883zs\F2_\8DFk\8Bh \00\8C\DCw\D3R\B5+6X\BA\B2\C4j\AB0\B4\FCMw\C2I\8E\9B\E3\A9~9u\FA\D3l\80\C8%p\EE\FDn2� \00$\FEj\C4e\A9\DB\~\95\A7\A5\80EK\BB\8DDsP\00@@AD'k\CF\E8\DB\D2(\80\9AK\D3\85\D6lb\F2\BA\8C*\80\00)\95 59\A3R:\F3\CE"\B6\80\88\00\00i1u4�\E9\F2�\A6\A2\FACM\93WMb*\E0*\00\00\00\00\00(\A8\80\00\00\80\00\00\00\00\00\00\00\00\00\FF\D9 C/// """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 ast as _ast import io as _io import os as _os import collections __all__ = ["error", "open"] _BLOCKSIZE = 512 error = OSError class _Database(collections.MutableMapping): # 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() _io = _io # for _commit() def __init__(self, filebasename, mode, flag='c'): self._mode = mode self._readonly = (flag == 'r') # 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 + '.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 + '.dat' self._bakfile = filebasename + '.bak' # The index is an in-memory dict, mirroring the directory file. self._index = None # maps keys to (pos, siz) pairs # Handle the creation self._create(flag) self._update() def _create(self, flag): if flag == 'n': for filename in (self._datfile, self._bakfile, self._dirfile): try: _os.remove(filename) except OSError: pass # Mod by Jack: create data file if needed try: f = _io.open(self._datfile, 'r', encoding="Latin-1") except OSError: if flag not in ('c', 'n'): import warnings warnings.warn("The database file is missing, the " "semantics of the 'c' flag will be used.", DeprecationWarning, stacklevel=4) with _io.open(self._datfile, 'w', encoding="Latin-1") as f: self._chmod(self._datfile) else: f.close() # Read directory file into the in-memory index dict. def _update(self): self._index = {} try: f = _io.open(self._dirfile, 'r', encoding="Latin-1") except OSError: self._modified = not self._readonly else: self._modified = False with f: for line in f: line = line.rstrip() key, pos_and_siz_pair = _ast.literal_eval(line) key = key.encode('Latin-1') self._index[key] = pos_and_siz_pair # 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 or not self._modified: return # nothing to do try: self._os.unlink(self._bakfile) except OSError: pass try: self._os.rename(self._dirfile, self._bakfile) except OSError: pass with self._io.open(self._dirfile, 'w', encoding="Latin-1") as f: self._chmod(self._dirfile) for key, pos_and_siz_pair in self._index.items(): # Use Latin-1 since it has no qualms with any value in any # position; UTF-8, though, does care sometimes. entry = "%r, %r\n" % (key.decode('Latin-1'), pos_and_siz_pair) f.write(entry) sync = _commit def _verify_open(self): if self._index is None: raise error('DBM object has already been closed') def __getitem__(self, key): if isinstance(key, str): key = key.encode('utf-8') self._verify_open() pos, siz = self._index[key] # may raise KeyError with _io.open(self._datfile, 'rb') as f: f.seek(pos) dat = f.read(siz) 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): with _io.open(self._datfile, 'rb+') as f: f.seek(0, 2) pos = int(f.tell()) npos = ((pos + _BLOCKSIZE - 1) // _BLOCKSIZE) * _BLOCKSIZE f.write(b'\0'*(npos-pos)) pos = npos f.write(val) 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): with _io.open(self._datfile, 'rb+') as f: f.seek(pos) f.write(val) 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 with _io.open(self._dirfile, 'a', encoding="Latin-1") as f: self._chmod(self._dirfile) f.write("%r, %r\n" % (key.decode("Latin-1"), pos_and_siz_pair)) def __setitem__(self, key, val): if self._readonly: import warnings warnings.warn('The database is opened for reading only', DeprecationWarning, stacklevel=2) if isinstance(key, str): key = key.encode('utf-8') elif not isinstance(key, (bytes, bytearray)): raise TypeError("keys must be bytes or strings") if isinstance(val, str): val = val.encode('utf-8') elif not isinstance(val, (bytes, bytearray)): raise TypeError("values must be bytes or strings") self._verify_open() self._modified = True 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): if self._readonly: import warnings warnings.warn('The database is opened for reading only', DeprecationWarning, stacklevel=2) if isinstance(key, str): key = key.encode('utf-8') self._verify_open() self._modified = True # 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): try: return list(self._index) except TypeError: raise error('DBM object has already been closed') from None def items(self): self._verify_open() return [(key, self[key]) for key in self._index.keys()] def __contains__(self, key): if isinstance(key, str): key = key.encode('utf-8') try: return key in self._index except TypeError: if self._index is None: raise error('DBM object has already been closed') from None else: raise def iterkeys(self): try: return iter(self._index) except TypeE