unpacker.tell() like in file.tell() #76

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1. jnothman commented on Oct 15, 2013

   

   jnothman

   on Oct 15, 2013

   Contributor

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   This sort of low-level file tracking can be achieved through the write_bytes arg to Unpacker.unpack, Unpacker.skip, etc. For example:

   class StreamCounter(object)
       __slots__ = ('nbytes',)
       def __init__(self):
           self.nbytes = 0
       def __call__(self, s):
           self.nbytes += len(s)
   
   unpacker = msgpack.Unpacker(stream)
   counter = StreamCounter()
   while True:
       try:
           obj = unpacker.unpack(write_bytes=counter)
       except msgpack.OutOfData:
           break
       offset = counter.nbytes

   (Yes, it will be slower than if tell were natively supported.)
2. sirex commented on Oct 16, 2013

   

   sirex

   on Oct 16, 2013

   Author

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   @jnothman thanks, some how I missed this write_bytes parameter, and it solves my issue.

   Now, as a workaround I packb obj and count bytes in it, to get offset, but using write_bytes is much more efficient. Thank again.
3. sirex

   closed this as completedon Oct 16, 2013