[GitHub] tdomhan opened a new pull request #8334: Bugfix: Python 3 compatiblity during optimizer serialization.

[GitBox]

tdomhan opened a new pull request #8334: Bugfix: Python 3 compatiblity during 
optimizer serialization.
URL: https://github.com/apache/incubator-mxnet/pull/8334
 
 
   ## Description ##
   In python 3 `pickle.dumps` returns a `bytes` object (instead of the `str` 
object in python 2). The `c_str` function however expects a string (on which it 
will call `.encode`. The fix is to detect if the return value of `pickle.dumps` 
is not a `str`. This is only true in python 3. If so we manually convert the 
`bytes` object to `str`.
   
   This is the full stack trace before the change:
   ```
   [ERROR:__main__] UNCAUGHT EXCEPTION
   Traceback (most recent call last):
     File "/opt/conda/lib/python3.6/runpy.py", line 193, in _run_module_as_main
       "__main__", mod_spec)
     File "/opt/conda/lib/python3.6/runpy.py", line 85, in _run_code
       exec(code, run_globals)
     File "/opt/conda/lib/python3.6/site-packages/sockeye/train.py", line 450, 
in <module>
       main()
     File "/opt/conda/lib/python3.6/site-packages/sockeye/train.py", line 446, 
in main
       mxmonitor_stat_func=args.monitor_stat_func)
     File "/opt/conda/lib/python3.6/site-packages/sockeye/training.py", line 
218, in fit
       self.module.init_optimizer(kvstore=kvstore, optimizer=optimizer, 
optimizer_params=optimizer_params)
     File 
"/opt/conda/lib/python3.6/site-packages/mxnet-0.12.0-py3.6.egg/mxnet/module/bucketing_module.py",
 line 385, in init_optimizer
       force_init=force_init)
     File 
"/opt/conda/lib/python3.6/site-packages/mxnet-0.12.0-py3.6.egg/mxnet/module/module.py",
 line 531, in init_optimizer
       kvstore.set_optimizer(self._optimizer)
     File 
"/opt/conda/lib/python3.6/site-packages/mxnet-0.12.0-py3.6.egg/mxnet/kvstore.py",
 line 394, in set_optimizer
       self._send_command_to_servers(0, optim_str)
     File 
"/opt/conda/lib/python3.6/site-packages/mxnet-0.12.0-py3.6.egg/mxnet/kvstore.py",
 line 532, in _send_command_to_servers
       self.handle, mx_uint(head), c_str(body)))
     File 
"/opt/conda/lib/python3.6/site-packages/mxnet-0.12.0-py3.6.egg/mxnet/base.py", 
line 189, in c_str
       return ctypes.c_char_p(string.encode('utf-8'))
   AttributeError: 'bytes' object has no attribute 'encode'
   ```

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