merges all those payments, along with those for any addresses which are all tiny payments, to a single txout. Got from https://people.xiph.org/~greg/groomer.py

merge tiny payment

#!/usr/bin/python
# simple cleanup script, 2012-12-25 <[email protected]>
import sys
import operator
from decimal import *
from jsonrpc import ServiceProxy
if len(sys.argv)<3:
  print 'Usage %s http://user:[email protected]:8332/ [fee]'%(sys.argv[0])
  print 'This script generates a transaction to cleanup your wallet.'
  print '  It looks for the single addresses which have the most small confirmed payments made to them and merges'
  print '   all those payments, along with those for any addresses which are all tiny payments, to a single txout.'
  print '  It must connect to bitcoin to inspect your wallet and to get fresh addresses to pay your coin to.'
  print '  This script doesn\'t sign or send the transaction, it only generates the raw txn for you.'
else:
  try:
    b = ServiceProxy(sys.argv[1])
    b.getinfo()
  except: 
    print "Couldn't connect to bitcoin"
    exit(1)
  min_fee=Decimal(sys.argv[2])

  #Add up the number of small txouts and amounts assigned to each address.
  coins=b.listunspent(1,99999999)
  scripts={}
  for coin in coins:
    script=coin['scriptPubKey']
    if script not in scripts:
      scripts[script]=(0,Decimal(0),0)
    if (coin['amount']<Decimal(25) and coin['amount']>=Decimal(0.01) and coin['confirmations']>100):
      scripts[script]=(scripts[script][0]+1,scripts[script][1]+coin['amount'],scripts[script][0]+1)
    else:
      scripts[script]=(scripts[script][0],scripts[script][1]+coin['amount'],scripts[script][0]+1)

  #which script has the largest number of well confirmed small but not dust outputs?
  most_overused = max(scripts.iteritems(), key=operator.itemgetter(1))[0]

  #If the best we can do doesn't reduce the number of txouts or just moves dust, give up.  
  if(scripts[most_overused][2]<3 or scripts[most_overused][1]<Decimal(0.01)):
    print "Wallet already clean."
    exit(0)
    
  usescripts=set([most_overused])

  #Also merge in scripts that are all dust, since they can't be spent without merging with something.
  for script in scripts.keys():
    if scripts[script][1]<Decimal(0.00010000):
      usescripts.add(script)
  
  amt=Decimal(0)
  txouts=[]
  for coin in coins:
    if coin['scriptPubKey'] in usescripts:
      amt+=coin['amount']
      txout={}
      txout['txid']=coin['txid']
      txout['vout']=coin['vout']
      txouts.append(txout)
  print 'Creating tx from %d inputs of total value %s:'%(len(txouts),amt)
  for script in usescripts:
    print '  Script %s has %d txins and %s BTC value.'%(script,scripts[script][2],str(scripts[script][1]))

  out={}
  na=amt-min_fee
  #One new output per 100 BTC of value to avoid consolidating too much value in too few addresses. 
  # But don't add an extra output if it would have less than 10 BTC.
  while na>0:
    amount=min(Decimal(100),na)
    if ((na-amount)<10):
      amount=na
    addr=b.getnewaddress('consolidate')
    #omg wtf, this is awful. the python-bitcoin crap makes the argument be a float
    if (Decimal(str(float(amount)))>0):
      if addr not in out:
        out[addr]=float(0)
      out[addr]+=float(amount)
    na-=Decimal(str(float(amount)))
  print 'Paying %s BTC (%s fee) to:'%(sum([Decimal(str(out[k])) for k in out.keys()]),amt-sum([Decimal(str(out[k])) for k in out.keys()]))
  for o in out.keys():
    print '  %s %s'%(o,out[o])
  
  txn=b.createrawtransaction(txouts,out)
  print '\nRaw transaction, sign with signrawtransaction then send with sendrawtransaction:'
  print 'If, after signing, transaction is too large (e.g. >20,000 character) you may need to provide a fee or it will be rejected by bitcoin.\n'
  print txn

#This could sign and send the transaction, but better to let the user do it.
#  txn=b.signrawtransaction(txn)
#  print txn
#  print 'Bytes: %d Fee: %s'%(len(txn['hex'])/2,amt-sum([Decimal(str(out[x])) for x in out.keys()]))