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#!/usr/bin/env python
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""" PickleShare - a small 'shelve' like datastore with concurrency support
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Like shelve, a PickleShareDB object acts like a normal dictionary. Unlike
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shelve, many processes can access the database simultaneously. Changing a
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value in database is immediately visible to other processes accessing the
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same database.
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Concurrency is possible because the values are stored in separate files. Hence
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the "database" is a directory where *all* files are governed by PickleShare.
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Example usage::
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from pickleshare import *
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db = PickleShareDB('~/testpickleshare')
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db.clear()
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print "Should be empty:",db.items()
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db['hello'] = 15
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db['aku ankka'] = [1,2,313]
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db['paths/are/ok/key'] = [1,(5,46)]
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print db.keys()
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del db['aku ankka']
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This module is certainly not ZODB, but can be used for low-load
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(non-mission-critical) situations where tiny code size trumps the
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advanced features of a "real" object database.
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Installation guide: easy_install pickleshare
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Author: Ville Vainio <vivainio@gmail.com>
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License: MIT open source license.
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"""
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from path import path as Path
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import os,stat,time
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import cPickle as pickle
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import UserDict
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import warnings
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import glob
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class PickleShareDB(UserDict.DictMixin):
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""" The main 'connection' object for PickleShare database """
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def __init__(self,root):
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""" Return a db object that will manage the specied directory"""
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self.root = Path(root).expanduser().abspath()
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if not self.root.isdir():
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self.root.makedirs()
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# cache has { 'key' : (obj, orig_mod_time) }
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self.cache = {}
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def __getitem__(self,key):
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""" db['key'] reading """
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fil = self.root / key
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try:
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mtime = (fil.stat()[stat.ST_MTIME])
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except OSError:
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raise KeyError(key)
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if fil in self.cache and mtime == self.cache[fil][1]:
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return self.cache[fil][0]
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try:
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# The cached item has expired, need to read
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obj = pickle.load(fil.open())
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except:
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raise KeyError(key)
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self.cache[fil] = (obj,mtime)
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return obj
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def __setitem__(self,key,value):
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""" db['key'] = 5 """
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fil = self.root / key
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parent = fil.parent
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if parent and not parent.isdir():
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parent.makedirs()
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pickled = pickle.dump(value,fil.open('w'))
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try:
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self.cache[fil] = (value,fil.mtime)
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except OSError,e:
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if e.errno != 2:
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raise
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def __delitem__(self,key):
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""" del db["key"] """
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fil = self.root / key
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self.cache.pop(fil,None)
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try:
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fil.remove()
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except OSError:
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# notfound and permission denied are ok - we
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# lost, the other process wins the conflict
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pass
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def _normalized(self, p):
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""" Make a key suitable for user's eyes """
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return str(self.root.relpathto(p)).replace('\\','/')
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def keys(self, globpat = None):
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""" All keys in DB, or all keys matching a glob"""
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if globpat is None:
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files = self.root.walkfiles()
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else:
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files = [Path(p) for p in glob.glob(self.root/globpat)]
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return [self._normalized(p) for p in files if p.isfile()]
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def uncache(self,*items):
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""" Removes all, or specified items from cache
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Use this after reading a large amount of large objects
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to free up memory, when you won't be needing the objects
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for a while.
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"""
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if not items:
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self.cache = {}
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for it in items:
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self.cache.pop(it,None)
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def waitget(self,key, maxwaittime = 60 ):
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""" Wait (poll) for a key to get a value
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Will wait for `maxwaittime` seconds before raising a KeyError.
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The call exits normally if the `key` field in db gets a value
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within the timeout period.
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Use this for synchronizing different processes or for ensuring
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that an unfortunately timed "db['key'] = newvalue" operation
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in another process (which causes all 'get' operation to cause a
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KeyError for the duration of pickling) won't screw up your program
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logic.
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"""
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wtimes = [0.2] * 3 + [0.5] * 2 + [1]
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tries = 0
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waited = 0
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while 1:
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try:
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val = self[key]
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return val
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except KeyError:
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pass
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if waited > maxwaittime:
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raise KeyError(key)
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time.sleep(wtimes[tries])
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waited+=wtimes[tries]
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if tries < len(wtimes) -1:
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tries+=1
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def getlink(self,folder):
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""" Get a convenient link for accessing items """
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return PickleShareLink(self, folder)
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def __repr__(self):
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return "PickleShareDB('%s')" % self.root
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class PickleShareLink:
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""" A shortdand for accessing nested PickleShare data conveniently.
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Created through PickleShareDB.getlink(), example::
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lnk = db.getlink('myobjects/test')
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lnk.foo = 2
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lnk.bar = lnk.foo + 5
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"""
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def __init__(self, db, keydir ):
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self.__dict__.update(locals())
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def __getattr__(self,key):
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return self.__dict__['db'][self.__dict__['keydir']+'/' + key]
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def __setattr__(self,key,val):
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self.db[self.keydir+'/' + key] = val
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def __repr__(self):
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db = self.__dict__['db']
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keys = db.keys( self.__dict__['keydir'] +"/*")
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return "<PickleShareLink '%s': %s>" % (
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self.__dict__['keydir'],
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";".join([Path(k).basename() for k in keys]))
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def test():
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db = PickleShareDB('~/testpickleshare')
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db.clear()
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print "Should be empty:",db.items()
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db['hello'] = 15
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db['aku ankka'] = [1,2,313]
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db['paths/nest/ok/keyname'] = [1,(5,46)]
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print db.keys()
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print db.keys('paths/nest/ok/k*')
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print dict(db) # snapsot of whole db
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db.uncache() # frees memory, causes re-reads later
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# shorthand for accessing deeply nested files
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lnk = db.getlink('myobjects/test')
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lnk.foo = 2
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lnk.bar = lnk.foo + 5
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print lnk.bar # 7
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def stress():
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db = PickleShareDB('~/fsdbtest')
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import time,sys
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for i in range(1000):
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for j in range(300):
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if i % 15 == 0 and i < 200:
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if str(j) in db:
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del db[str(j)]
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continue
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if j%33 == 0:
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time.sleep(0.02)
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db[str(j)] = db.get(str(j), []) + [(i,j,"proc %d" % os.getpid())]
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print i,
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sys.stdout.flush()
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if i % 10 == 0:
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db.uncache()
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def main():
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import textwrap
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usage = textwrap.dedent("""\
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pickleshare - manage PickleShare databases
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Usage:
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pickleshare dump /path/to/db > dump.txt
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pickleshare load /path/to/db < dump.txt
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pickleshare test /path/to/db
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""")
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DB = PickleShareDB
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import sys
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if len(sys.argv) < 2:
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print usage
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return
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cmd = sys.argv[1]
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args = sys.argv[2:]
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if cmd == 'dump':
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if not args: args= ['.']
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db = DB(args[0])
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import pprint
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pprint.pprint(db.items())
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elif cmd == 'load':
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cont = sys.stdin.read()
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db = DB(args[0])
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data = eval(cont)
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db.clear()
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for k,v in db.items():
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db[k] = v
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elif cmd == 'testwait':
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db = DB(args[0])
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db.clear()
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print db.waitget('250')
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elif cmd == 'test':
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test()
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stress()
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if __name__== "__main__":
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main()
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