Guido van Rossum | 9f824a7 | 1995-08-10 19:29:28 +0000 | [diff] [blame] | 1 | """A dumb and slow but simple dbm clone. |
| 2 | |
| 3 | For database spam, spam.dir contains the index (a text file), |
| 4 | spam.bak *may* contain a backup of the index (also a text file), |
| 5 | while spam.dat contains the data (a binary file). |
| 6 | |
| 7 | XXX TO DO: |
| 8 | |
| 9 | - seems to contain a bug when updating... |
| 10 | |
| 11 | - reclaim free space (currently, space once occupied by deleted or expanded |
| 12 | items is never reused) |
| 13 | |
| 14 | - support concurrent access (currently, if two processes take turns making |
| 15 | updates, they can mess up the index) |
| 16 | |
| 17 | - support efficient access to large databases (currently, the whole index |
| 18 | is read when the database is opened, and some updates rewrite the whole index) |
| 19 | |
| 20 | - support opening for read-only (flag = 'm') |
| 21 | |
| 22 | """ |
| 23 | |
Martin v. Löwis | d0cd95c | 2001-07-19 10:06:39 +0000 | [diff] [blame] | 24 | import os as _os |
Guido van Rossum | 9f824a7 | 1995-08-10 19:29:28 +0000 | [diff] [blame] | 25 | import __builtin__ |
| 26 | |
| 27 | _open = __builtin__.open |
| 28 | |
| 29 | _BLOCKSIZE = 512 |
| 30 | |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 31 | error = IOError # For anydbm |
Guido van Rossum | 22a1890 | 1996-05-28 22:58:40 +0000 | [diff] [blame] | 32 | |
Guido van Rossum | 9f824a7 | 1995-08-10 19:29:28 +0000 | [diff] [blame] | 33 | class _Database: |
| 34 | |
Fred Drake | 2c8373b | 2001-12-07 21:54:46 +0000 | [diff] [blame] | 35 | def __init__(self, file, mode): |
| 36 | self._mode = mode |
Guido van Rossum | e2ae77b | 2001-10-24 20:42:55 +0000 | [diff] [blame] | 37 | self._dirfile = file + _os.extsep + 'dir' |
| 38 | self._datfile = file + _os.extsep + 'dat' |
| 39 | self._bakfile = file + _os.extsep + 'bak' |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 40 | # Mod by Jack: create data file if needed |
| 41 | try: |
| 42 | f = _open(self._datfile, 'r') |
| 43 | except IOError: |
Fred Drake | 2c8373b | 2001-12-07 21:54:46 +0000 | [diff] [blame] | 44 | f = _open(self._datfile, 'w', self._mode) |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 45 | f.close() |
| 46 | self._update() |
Guido van Rossum | 9f824a7 | 1995-08-10 19:29:28 +0000 | [diff] [blame] | 47 | |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 48 | def _update(self): |
| 49 | self._index = {} |
| 50 | try: |
| 51 | f = _open(self._dirfile) |
| 52 | except IOError: |
| 53 | pass |
| 54 | else: |
| 55 | while 1: |
| 56 | line = f.readline().rstrip() |
| 57 | if not line: break |
| 58 | key, (pos, siz) = eval(line) |
| 59 | self._index[key] = (pos, siz) |
| 60 | f.close() |
| 61 | |
| 62 | def _commit(self): |
| 63 | try: _os.unlink(self._bakfile) |
| 64 | except _os.error: pass |
| 65 | try: _os.rename(self._dirfile, self._bakfile) |
| 66 | except _os.error: pass |
Fred Drake | 2c8373b | 2001-12-07 21:54:46 +0000 | [diff] [blame] | 67 | f = _open(self._dirfile, 'w', self._mode) |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 68 | for key, (pos, siz) in self._index.items(): |
| 69 | f.write("%s, (%s, %s)\n" % (`key`, `pos`, `siz`)) |
| 70 | f.close() |
| 71 | |
| 72 | def __getitem__(self, key): |
| 73 | pos, siz = self._index[key] # may raise KeyError |
| 74 | f = _open(self._datfile, 'rb') |
| 75 | f.seek(pos) |
| 76 | dat = f.read(siz) |
| 77 | f.close() |
| 78 | return dat |
| 79 | |
| 80 | def _addval(self, val): |
| 81 | f = _open(self._datfile, 'rb+') |
| 82 | f.seek(0, 2) |
| 83 | pos = int(f.tell()) |
Guido van Rossum | 9f824a7 | 1995-08-10 19:29:28 +0000 | [diff] [blame] | 84 | ## Does not work under MW compiler |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 85 | ## pos = ((pos + _BLOCKSIZE - 1) / _BLOCKSIZE) * _BLOCKSIZE |
| 86 | ## f.seek(pos) |
Guido van Rossum | 54e54c6 | 2001-09-04 19:14:14 +0000 | [diff] [blame] | 87 | npos = ((pos + _BLOCKSIZE - 1) // _BLOCKSIZE) * _BLOCKSIZE |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 88 | f.write('\0'*(npos-pos)) |
| 89 | pos = npos |
| 90 | |
| 91 | f.write(val) |
| 92 | f.close() |
| 93 | return (pos, len(val)) |
| 94 | |
| 95 | def _setval(self, pos, val): |
| 96 | f = _open(self._datfile, 'rb+') |
| 97 | f.seek(pos) |
| 98 | f.write(val) |
| 99 | f.close() |
| 100 | return (pos, len(val)) |
| 101 | |
| 102 | def _addkey(self, key, (pos, siz)): |
| 103 | self._index[key] = (pos, siz) |
Fred Drake | 2c8373b | 2001-12-07 21:54:46 +0000 | [diff] [blame] | 104 | f = _open(self._dirfile, 'a', self._mode) |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 105 | f.write("%s, (%s, %s)\n" % (`key`, `pos`, `siz`)) |
| 106 | f.close() |
| 107 | |
| 108 | def __setitem__(self, key, val): |
| 109 | if not type(key) == type('') == type(val): |
| 110 | raise TypeError, "keys and values must be strings" |
| 111 | if not self._index.has_key(key): |
| 112 | (pos, siz) = self._addval(val) |
| 113 | self._addkey(key, (pos, siz)) |
| 114 | else: |
| 115 | pos, siz = self._index[key] |
| 116 | oldblocks = (siz + _BLOCKSIZE - 1) / _BLOCKSIZE |
| 117 | newblocks = (len(val) + _BLOCKSIZE - 1) / _BLOCKSIZE |
| 118 | if newblocks <= oldblocks: |
| 119 | pos, siz = self._setval(pos, val) |
| 120 | self._index[key] = pos, siz |
| 121 | else: |
| 122 | pos, siz = self._addval(val) |
| 123 | self._index[key] = pos, siz |
| 124 | |
| 125 | def __delitem__(self, key): |
| 126 | del self._index[key] |
| 127 | self._commit() |
| 128 | |
| 129 | def keys(self): |
| 130 | return self._index.keys() |
| 131 | |
| 132 | def has_key(self, key): |
| 133 | return self._index.has_key(key) |
| 134 | |
Fred Drake | a7cc69e | 2001-05-03 04:55:47 +0000 | [diff] [blame] | 135 | def __contains__(self, key): |
| 136 | return self._index.has_key(key) |
| 137 | |
| 138 | def iterkeys(self): |
| 139 | return self._index.iterkeys() |
| 140 | __iter__ = iterkeys |
| 141 | |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 142 | def __len__(self): |
| 143 | return len(self._index) |
| 144 | |
| 145 | def close(self): |
Anthony Baxter | ed90570 | 2001-12-21 05:13:37 +0000 | [diff] [blame] | 146 | self._commit() |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 147 | self._index = None |
| 148 | self._datfile = self._dirfile = self._bakfile = None |
Guido van Rossum | 9f824a7 | 1995-08-10 19:29:28 +0000 | [diff] [blame] | 149 | |
Anthony Baxter | ed90570 | 2001-12-21 05:13:37 +0000 | [diff] [blame] | 150 | def __del__(self): |
| 151 | if self._index is not None: |
| 152 | self._commit() |
| 153 | |
| 154 | |
Guido van Rossum | 9f824a7 | 1995-08-10 19:29:28 +0000 | [diff] [blame] | 155 | |
Fred Drake | 2c8373b | 2001-12-07 21:54:46 +0000 | [diff] [blame] | 156 | def open(file, flag=None, mode=0666): |
Tim Peters | 88869f9 | 2001-01-14 23:36:06 +0000 | [diff] [blame] | 157 | # flag, mode arguments are currently ignored |
Fred Drake | 2c8373b | 2001-12-07 21:54:46 +0000 | [diff] [blame] | 158 | return _Database(file, mode) |