try fix

error: unpack requires a string argument of length 4

Author: siddontang

pymysqlreplication/bitmap.py

@@ -68,14 +68,14 @@ def _createLastWordMask(self):
  b = bytearray(struct.pack("<I", self._lastWordMask))
  b[3] = mask
 
- self._lastWordMask = struct.unpack("<I", b)[0]
+ self._lastWordMask = struct.unpack("<I", bytes(b))[0]
 
  def bits_set(self):
  res = 0
  for i in range(0, int(len(self._bitmap) / 4) - 1):
- res += self._countBitsUint32(struct.unpack("<I", self._bitmap[i*4:i*4 + 4])[0])
+ res += self._countBitsUint32(struct.unpack("<I", bytes(self._bitmap[i*4:i*4 + 4]))[0])
 
- res += self._countBitsUint32(struct.unpack("<I", self._bitmap[-4:])[0] & ~self._lastWordMask)
+ res += self._countBitsUint32(struct.unpack("<I", bytes(self._bitmap[-4:]))[0] & ~self._lastWordMask)
 
  return res