message: Set default initialSize for Builder to 0
  * Set default initialSize for Builder to 0
  * Change default size of builder to 1024.
  This matches what the C++ and Java versions do.
diff: @@ -113,7 +113,7 @@ class Builder(object):
  MAX_BUFFER_SIZE = 2**31
  ## @endcond
  - def __init__(self, initialSize):
  + def __init__(self, initialSize=1024):
  """Initializes a Builder of size `initial_size`.
  The internal buffer is grown as needed.
  