[yt-dev] Issue #816: mpi4py is not imported properly in parallel_analysis_interface.py (yt_analysis/yt)

[Kacper Kowalik]

New issue 816: mpi4py is not imported properly in parallel_analysis_interface.py
https://bitbucket.org/yt_analysis/yt/issue/816/mpi4py-is-not-imported-properly-in

Kacper Kowalik:

Revision fec39112bec causes:

```
#!text

$ python -c 'import yt.utilities.parallel_tools.parallel_analysis_interface'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "yt/__init__.py", line 116, in <module>
    from yt.data_objects.api import \
  File "yt/data_objects/api.py", line 16, in <module>
    from grid_patch import \
  File "yt/data_objects/grid_patch.py", line 25, in <module>
    from yt.data_objects.data_containers import \
  File "yt/data_objects/data_containers.py", line 32, in <module>
    from yt.utilities.parallel_tools.parallel_analysis_interface import \
  File "yt/utilities/parallel_tools/parallel_analysis_interface.py", line 1015, in <module>
    communication_system = CommunicationSystem()
  File "yt/utilities/parallel_tools/parallel_analysis_interface.py", line 587, in __init__
    self.communicators.append(Communicator(MPI.COMM_WORLD))
NameError: global name 'MPI' is not defined
```

Responsible: xarthisius