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145 lines
4.0 KiB
Python
145 lines
4.0 KiB
Python
"""A dumb and slow but simple dbm clone.
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For database spam, spam.dir contains the index (a text file),
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spam.bak *may* contain a backup of the index (also a text file),
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while spam.dat contains the data (a binary file).
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XXX TO DO:
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- seems to contain a bug when updating...
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- reclaim free space (currently, space once occupied by deleted or expanded
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items is never reused)
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- support concurrent access (currently, if two processes take turns making
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updates, they can mess up the index)
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- support efficient access to large databases (currently, the whole index
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is read when the database is opened, and some updates rewrite the whole index)
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- support opening for read-only (flag = 'm')
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"""
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_os = __import__('os')
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import __builtin__
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_open = __builtin__.open
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_BLOCKSIZE = 512
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error = IOError # For anydbm
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class _Database:
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def __init__(self, file):
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self._dirfile = file + '.dir'
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self._datfile = file + '.dat'
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self._bakfile = file + '.bak'
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# Mod by Jack: create data file if needed
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try:
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f = _open(self._datfile, 'r')
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except IOError:
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f = _open(self._datfile, 'w')
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f.close()
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self._update()
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def _update(self):
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self._index = {}
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try:
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f = _open(self._dirfile)
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except IOError:
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pass
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else:
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while 1:
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line = f.readline().rstrip()
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if not line: break
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key, (pos, siz) = eval(line)
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self._index[key] = (pos, siz)
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f.close()
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def _commit(self):
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try: _os.unlink(self._bakfile)
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except _os.error: pass
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try: _os.rename(self._dirfile, self._bakfile)
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except _os.error: pass
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f = _open(self._dirfile, 'w')
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for key, (pos, siz) in self._index.items():
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f.write("%s, (%s, %s)\n" % (`key`, `pos`, `siz`))
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f.close()
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def __getitem__(self, key):
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pos, siz = self._index[key] # may raise KeyError
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f = _open(self._datfile, 'rb')
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f.seek(pos)
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dat = f.read(siz)
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f.close()
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return dat
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def _addval(self, val):
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f = _open(self._datfile, 'rb+')
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f.seek(0, 2)
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pos = int(f.tell())
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## Does not work under MW compiler
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## pos = ((pos + _BLOCKSIZE - 1) / _BLOCKSIZE) * _BLOCKSIZE
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## f.seek(pos)
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npos = ((pos + _BLOCKSIZE - 1) / _BLOCKSIZE) * _BLOCKSIZE
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f.write('\0'*(npos-pos))
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pos = npos
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f.write(val)
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f.close()
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return (pos, len(val))
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def _setval(self, pos, val):
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f = _open(self._datfile, 'rb+')
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f.seek(pos)
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f.write(val)
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f.close()
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return (pos, len(val))
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def _addkey(self, key, (pos, siz)):
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self._index[key] = (pos, siz)
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f = _open(self._dirfile, 'a')
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f.write("%s, (%s, %s)\n" % (`key`, `pos`, `siz`))
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f.close()
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def __setitem__(self, key, val):
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if not type(key) == type('') == type(val):
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raise TypeError, "keys and values must be strings"
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if not self._index.has_key(key):
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(pos, siz) = self._addval(val)
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self._addkey(key, (pos, siz))
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else:
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pos, siz = self._index[key]
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oldblocks = (siz + _BLOCKSIZE - 1) / _BLOCKSIZE
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newblocks = (len(val) + _BLOCKSIZE - 1) / _BLOCKSIZE
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if newblocks <= oldblocks:
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pos, siz = self._setval(pos, val)
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self._index[key] = pos, siz
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else:
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pos, siz = self._addval(val)
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self._index[key] = pos, siz
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def __delitem__(self, key):
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del self._index[key]
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self._commit()
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def keys(self):
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return self._index.keys()
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def has_key(self, key):
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return self._index.has_key(key)
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def __len__(self):
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return len(self._index)
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def close(self):
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self._index = None
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self._datfile = self._dirfile = self._bakfile = None
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def open(file, flag = None, mode = None):
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# flag, mode arguments are currently ignored
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return _Database(file)
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