Python 3.5: TypeError, "is not JSON serializable"

[pierrelux]

While trying to run examples/agents/random_agent.py from 7b91967 with Python 3.5.1, I get:

Traceback (most recent call last):
  File "examples/agents/random_agent.py", line 36, in <module>
    ob = env.reset()
  File "/home/pierre-luc/anaconda3/lib/python3.5/site-packages/gym-0.0.7-py3.5.egg/gym/core.py", line 96, in reset
    self.monitor._after_reset(observation)
  File "/home/pierre-luc/anaconda3/lib/python3.5/site-packages/gym-0.0.7-py3.5.egg/gym/monitoring/monitor.py", line 228, in _after_reset
    self._close_video_recorder()
  File "/home/pierre-luc/anaconda3/lib/python3.5/site-packages/gym-0.0.7-py3.5.egg/gym/monitoring/monitor.py", line 243, in _close_video_recorder
    self.video_recorder.close()
  File "/home/pierre-luc/anaconda3/lib/python3.5/site-packages/gym-0.0.7-py3.5.egg/gym/monitoring/video_recorder.py", line 144, in close
    self.write_metadata()
  File "/home/pierre-luc/anaconda3/lib/python3.5/site-packages/gym-0.0.7-py3.5.egg/gym/monitoring/video_recorder.py", line 150, in write_metadata
    json.dump(self.metadata, f)
  File "/home/pierre-luc/anaconda3/lib/python3.5/json/__init__.py", line 178, in dump
    for chunk in iterable:
  File "/home/pierre-luc/anaconda3/lib/python3.5/json/encoder.py", line 429, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "/home/pierre-luc/anaconda3/lib/python3.5/json/encoder.py", line 403, in _iterencode_dict
    yield from chunks
  File "/home/pierre-luc/anaconda3/lib/python3.5/json/encoder.py", line 403, in _iterencode_dict
    yield from chunks
  File "/home/pierre-luc/anaconda3/lib/python3.5/json/encoder.py", line 436, in _iterencode
    o = _default(o)
  File "/home/pierre-luc/anaconda3/lib/python3.5/json/encoder.py", line 180, in default
    raise TypeError(repr(o) + " is not JSON serializable")
TypeError: b'avconv 9.18-6:9.18-0ubuntu0.14.04.1\nlibavutil     52.  3. 0 / 52.  3. 0\nlibavcodec    54. 35. 0 / 54. 35. 0\nlibavformat   54. 20. 4 / 54. 20. 4\nlibavdevice   53.  2. 0 / 53.  2. 0\nlibavfi
lter    3.  3. 0 /  3.  3. 0\nlibavresample  1.  0. 1 /  1.  0. 1\nlibswscale     2.  1. 1 /  2.  1. 1\n' is not JSON serializable

The error is due to the fact that subprocess.check_output on line 257 of gym/monitoring/video_recording.py returns a bytes string but json.dump expects a str type.

I fixed the problem on my system with str() on the output of check_output:

@property
def version_info(self):
    return {'backend':self.backend,'version': str(subprocess.check_output([self.backend, '-version'])),'cmdline':self.cmdline}

There is a probably a better way to fix this problem portably using six.

[gdb]

(Thanks, we'll fix it!)