'''Alternate DB based on a dict subclass
Runs like gdbm's fast mode (all writes all delayed until close).
While open, the whole dict is kept in memory. Start-up and
close time's are potentially long because the whole dict must be
read or written to disk.
Input file format is automatically discovered.
Output file format is selectable between pickle, json, and csv.
All three are backed by fast C implementations.
'''
import pickle, json, csv
import os, shutil
class DictDB(dict):
def __init__(self, filename, flag=None, mode=None, format=None, *args, **kwds):
self.flag = flag or 'c' # r=readonly, c=create, or n=new
self.mode = mode # None or octal triple like 0x666
self.format = format or 'csv' # csv, json, or pickle
self.filename = filename
if flag != 'n' and os.access(filename, os.R_OK):
file = __builtins__.open(filename, 'rb')
try:
self.load(file)
finally:
file.close()
self.update(*args, **kwds)
def sync(self):
if self.flag == 'r':
return
filename = self.filename
tempname = filename + '.tmp'
file = __builtins__.open(tempname, 'wb')
try:
self.dump(file)
except Exception:
file.close()
os.remove(tempname)
raise
file.close()
shutil.move(tempname, self.filename) # atomic commit
if self.mode is not None:
os.chmod(self.filename, self.mode)
def close(self):
self.sync()
def dump(self, file):
if self.format == 'csv':
csv.writer(file).writerows(self.iteritems())
elif self.format == 'json':
json.dump(self, file, separators=(',', ':'))
elif self.format == 'pickle':
pickle.dump(self.items(), file, -1)
else:
raise NotImplementedError('Unknown format: %r' % self.format)
def load(self, file):
# try formats from most restrictive to least restrictive
for loader in (pickle.load, json.load, csv.reader):
file.seek(0)
try:
return self.update(loader(file))
except Exception:
pass
raise ValueError('File not in recognized format')
def dbopen(filename, flag=None, mode=None, format=None):
return DictDB(filename, flag, mode, format)
if __name__ == '__main__':
import random
os.chdir('/dbm_sqlite/alt')
print(os.getcwd())
s = dbopen('tmp.shl', 'c', format='json')
print(s, 'start')
s['abc'] = '123'
s['rand'] = random.randrange(10000)
s.close()
f = __builtins__.open('tmp.shl', 'rb')
print (f.read())
f.close()
