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authorGeorg Brandl <georg@python.org>2008-05-26 10:29:35 (GMT)
committerGeorg Brandl <georg@python.org>2008-05-26 10:29:35 (GMT)
commit0a7ac7d70d370544c6a9d118bbbd6886ad4f5ce5 (patch)
treeec61fd6d53e6425b8639567860140c724ea7bc63 /Lib/dumbdbm.py
parente6f00637be87c8f5f0e50bf317d684ea421a6d19 (diff)
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Create the dbm package from PEP 3108. #2881.
Diffstat (limited to 'Lib/dumbdbm.py')
-rw-r--r--Lib/dumbdbm.py255
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diff --git a/Lib/dumbdbm.py b/Lib/dumbdbm.py
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-"""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 io as _io
-import os as _os
-import collections
-
-_BLOCKSIZE = 512
-
-error = IOError # For anydbm
-
-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):
- 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 + '.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
-
- # Mod by Jack: create data file if needed
- try:
- f = _io.open(self._datfile, 'r')
- except IOError:
- f = _io.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 = _io.open(self._dirfile, 'r')
- 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._io.open(self._dirfile, 'w')
- self._chmod(self._dirfile)
- for key, pos_and_siz_pair in self._index.items():
- f.write("%r, %r\n" % (key, pos_and_siz_pair))
- f.close()
-
- sync = _commit
-
- def __getitem__(self, key):
- key = key.decode("latin-1")
- pos, siz = self._index[key] # may raise KeyError
- f = _io.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 = _io.open(self._datfile, 'rb+')
- 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)
- 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 = _io.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 = _io.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 isinstance(key, bytes):
- raise TypeError("keys must be bytes")
- key = key.decode("latin-1") # hashable bytes
- if not isinstance(val, (bytes, bytearray)):
- raise TypeError("values must be byte 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):
- key = key.decode("latin-1")
- # 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 [key.encode("latin-1") for key in self._index.keys()]
-
- def items(self):
- return [(key.encode("latin-1"), self[key.encode("latin-1")])
- for key in self._index.keys()]
-
- def __contains__(self, key):
- key = key.decode("latin-1")
- return key in self._index
-
- def iterkeys(self):
- return iter(self._index.keys())
- __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=0o666):
- """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 0o666 (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)