class IndexedDatabase:
"""A file of objects that are written sequentially and read randomly.
The objects are indexed by small non-negative integers, and a
RecordTable is used to store the index -> fileoffset map.
fileoffset=0 is used to represent an empty record. (An offset of 0
cannot occur for a legitimate record because the serializer is
written there.)
The main file consists of a sequence of pickles (or other serialized
data format). The zeroth record is a pickled Serializer.
Subsequent ones are objects serialized using the serializer. The
offset of each object in the file is stored to an index table so
that the data can later be retrieved randomly.
Objects are always stored to the end of the file. If an object is
deleted or overwritten, the fact is recorded in the index_table but
the space in the pickle file is not garbage collected. This has the
advantage that one can create a modified version of a database that
shares the main data file with an old version by copying the index
file. But it has the disadvantage that space is wasted whenever
objects are written multiple times."""
def __init__(self, filename, index_filename, mode, serializer=None):
"""Initialize an IndexedDatabase, writing the serializer if necessary.
SERIALIZER is only used if MODE is DB_OPEN_NEW; otherwise the
serializer is read from the file."""
self.filename = filename
self.index_filename = index_filename
self.mode = mode
if self.mode == DB_OPEN_NEW:
self.f = open(self.filename, 'wb+')
elif self.mode == DB_OPEN_WRITE:
self.f = open(self.filename, 'rb+')
elif self.mode == DB_OPEN_READ:
self.f = open(self.filename, 'rb')
else:
raise RuntimeError('Invalid mode %r' % self.mode)
self.index_table = RecordTable(self.index_filename, self.mode,
FileOffsetPacker())
if self.mode == DB_OPEN_NEW:
assert serializer is not None
self.serializer = serializer
cPickle.dump(self.serializer, self.f, -1)
else:
# Read the memo from the first pickle:
self.serializer = cPickle.load(self.f)
# Seek to the end of the file, and record that position:
self.f.seek(0, 2)
self.fp = self.f.tell()
self.eofp = self.fp
def __setitem__(self, index, item):
"""Write ITEM into the database indexed by INDEX."""
# Make sure we're at the end of the file:
if self.fp != self.eofp:
self.f.seek(self.eofp)
self.index_table[index] = self.eofp
s = self.serializer.dumps(item)
self.f.write(s)
self.eofp += len(s)
self.fp = self.eofp
def _fetch(self, offset):
if self.fp != offset:
self.f.seek(offset)
# There is no easy way to tell how much data will be read, so just
# indicate that we don't know the current file pointer:
self.fp = None
return self.serializer.loadf(self.f)
def iterkeys(self):
return self.index_table.iterkeys()
def itervalues(self):
for offset in self.index_table.itervalues():
yield self._fetch(offset)
def __getitem__(self, index):
offset = self.index_table[index]
return self._fetch(offset)
def get(self, item, default=None):
try:
return self[item]
except KeyError:
return default
def get_many(self, indexes, default=None):
"""Yield (index,item) tuples for INDEXES, in arbitrary order.
Yield (index,default) for indexes with no defined values."""
offsets = []
for (index, offset) in self.index_table.get_many(indexes):
if offset is None:
yield (index, default)
else:
offsets.append((offset, index))
# Sort the offsets to reduce disk seeking:
offsets.sort()
for (offset, index) in offsets:
yield (index, self._fetch(offset))
def __delitem__(self, index):
# We don't actually free the data in self.f.
del self.index_table[index]
def close(self):
self.index_table.close()
self.index_table = None
self.f.close()
self.f = None
def __str__(self):
return 'IndexedDatabase(%r)' % (self.filename, )
class IndexedDatabase:
"""A file of objects that are written sequentially and read randomly.
The objects are indexed by small non-negative integers, and a
RecordTable is used to store the index -> fileoffset map.
fileoffset=0 is used to represent an empty record. (An offset of 0
cannot occur for a legitimate record because the serializer is
written there.)
The main file consists of a sequence of pickles (or other serialized
data format). The zeroth record is a pickled Serializer.
Subsequent ones are objects serialized using the serializer. The
offset of each object in the file is stored to an index table so
that the data can later be retrieved randomly.
Objects are always stored to the end of the file. If an object is
deleted or overwritten, the fact is recorded in the index_table but
the space in the pickle file is not garbage collected. This has the
advantage that one can create a modified version of a database that
shares the main data file with an old version by copying the index
file. But it has the disadvantage that space is wasted whenever
objects are written multiple times."""
def __init__(self, filename, index_filename, mode, serializer=None):
"""Initialize an IndexedDatabase, writing the serializer if necessary.
SERIALIZER is only used if MODE is DB_OPEN_NEW; otherwise the
serializer is read from the file."""
self.filename = filename
self.index_filename = index_filename
self.mode = mode
if self.mode == DB_OPEN_NEW:
self.f = open(self.filename, 'wb+')
elif self.mode == DB_OPEN_WRITE:
self.f = open(self.filename, 'rb+')
elif self.mode == DB_OPEN_READ:
self.f = open(self.filename, 'rb')
else:
raise RuntimeError('Invalid mode %r' % self.mode)
self.index_table = RecordTable(
self.index_filename, self.mode, FileOffsetPacker()
)
if self.mode == DB_OPEN_NEW:
assert serializer is not None
self.serializer = serializer
cPickle.dump(self.serializer, self.f, -1)
else:
# Read the memo from the first pickle:
self.serializer = cPickle.load(self.f)
# Seek to the end of the file, and record that position:
self.f.seek(0, 2)
self.fp = self.f.tell()
self.eofp = self.fp
def __setitem__(self, index, item):
"""Write ITEM into the database indexed by INDEX."""
# Make sure we're at the end of the file:
if self.fp != self.eofp:
self.f.seek(self.eofp)
self.index_table[index] = self.eofp
s = self.serializer.dumps(item)
self.f.write(s)
self.eofp += len(s)
self.fp = self.eofp
def _fetch(self, offset):
if self.fp != offset:
self.f.seek(offset)
# There is no easy way to tell how much data will be read, so just
# indicate that we don't know the current file pointer:
self.fp = None
return self.serializer.loadf(self.f)
def iterkeys(self):
return self.index_table.iterkeys()
def itervalues(self):
for offset in self.index_table.itervalues():
yield self._fetch(offset)
def __getitem__(self, index):
offset = self.index_table[index]
return self._fetch(offset)
def get(self, item, default=None):
try:
return self[item]
except KeyError:
return default
def get_many(self, indexes, default=None):
"""Yield (index,item) tuples for INDEXES, in arbitrary order.
Yield (index,default) for indexes with no defined values."""
offsets = []
for (index, offset) in self.index_table.get_many(indexes):
if offset is None:
yield (index, default)
else:
offsets.append((offset, index))
# Sort the offsets to reduce disk seeking:
offsets.sort()
for (offset,index) in offsets:
yield (index, self._fetch(offset))
def __delitem__(self, index):
# We don't actually free the data in self.f.
del self.index_table[index]
def close(self):
self.index_table.close()
self.index_table = None
self.f.close()
self.f = None
def __str__(self):
return 'IndexedDatabase(%r)' % (self.filename,)
