mirror of https://github.com/python/cpython
126 lines
3.0 KiB
Python
126 lines
3.0 KiB
Python
"""A slow but simple dbm clone for the Mac.
|
|
|
|
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:
|
|
|
|
- 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)
|
|
"""
|
|
|
|
_os = __import__('os')
|
|
import __builtin__
|
|
|
|
_open = __builtin__.open
|
|
|
|
_BLOCKSIZE = 512
|
|
|
|
class _Database:
|
|
|
|
def __init__(self, file):
|
|
self._dirfile = file + '.dir'
|
|
self._datfile = file + '.dat'
|
|
self._bakfile = file + '.bak'
|
|
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()
|
|
pos = ((pos + _BLOCKSIZE - 1) / _BLOCKSIZE) * _BLOCKSIZE
|
|
f.seek(pos)
|
|
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, (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, "dbmac 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 = self._datfile = self._dirfile = self._bakfile = None
|
|
|
|
|
|
def open(file, mode = None):
|
|
return _Database(file)
|