new_contents: import hashlib
  import binascii
  import string
  prev_hash = "4d16b6f85af6e2198f44ae2a6de67f78487ae5611b77c6c0440b921e00000000"
  coinbase1 = "01000000010000000000000000000000000000000000000000000000000000000000000000ffffffff20020862062f503253482f04b8864e5008"
  coinbase2 = "072f736c7573682f000000000100f2052a010000001976a914d23fcdf86f7e756a64a7a9688ef9903327048ed988ac00000000"
  merkle_branch = []
  version = "00000002"
  nbits = "1c2ac4af"
  ntime = "504e86b9"
  extra_nonce1 = "55555555"
  extra_nonce2 = "aaaaaaaa"
  coinbase = coinbase1 + extra_nonce1 + extra_nonce2 + coinbase2
  
  merkle_branch = [
  "1111111111111111111111111111111111111111111111111111111111111111",
  "2222222222222222222222222222222222222222222222222222222222222222",
  "3333333333333333333333333333333333333333333333333333333333333333",
  "4444444444444444444444444444444444444444444444444444444444444444",
  "5555555555555555555555555555555555555555555555555555555555555555",
  ]
  
  #print len(coinbase1)
  #print coinbase,len(coinbase)
  coinbase_hash_bin = hashlib.sha256(hashlib.sha256(binascii.unhexlify(coinbase)).digest()).digest()
  #print binascii.hexlify(coinbase_hash_bin)
  def build_merkle_root(merkle_branch, coinbase_hash_bin):
      merkle_root = coinbase_hash_bin
      for h in merkle_branch:
          merkle_root = hashlib.sha256(hashlib.sha256(merkle_root + binascii.unhexlify(h)).digest()).digest()
      return binascii.hexlify(merkle_root)
  	
  print build_merkle_root(merkle_branch,coinbase_hash_bin)
  
  
subject: Add python code to verify doublesha256 calculating.