Properly use Python3's buffer interface.

[sceeter89]

Description

When using luigi with Python 3 there is issue running PigTask. Because output in track_and_progress is both read to unicode string and copied to temporary file, it failed as conversion to string happens before writing to file. I simply moved decoding after writing to temporary file.

Motivation and Context

Without this change, running PigTask ended with following error:

File "/projects/big-data/luigi-tasks/libs/pig_task.py", line 57, in on_execute
PigTask.run(self)
File "/home/etl/.projects/big-data/lib/python3.4/site-packages/luigi/contrib/pig.py", line 127, in run
self.track_and_progress(cmd)
File "/home/etl/.projects/big-data/lib/python3.4/site-packages/luigi/contrib/pig.py", line 149, in >track_and_progress
temp_stdout.write(line)
TypeError: 'str' does not support the buffer interface

And while Pig script finished successfully, luigi marked it as failed.

Have you tested this? If so, how?

After making this change locally our Pig scripts run without issues using Python3.4

[mention-bot]

@sceeter89, thanks for your PR! By analyzing the annotation information on this pull request, we identified @gpoulin, @jeremykarn and @toidi to be potential reviewers

[Tarrasch]

Can you add a test case?

[sceeter89]

I'll give it a shot afternoon.

[sceeter89]

@Tarrasch Instead of adding new test case I changed fake Popen stuff to let PigTask read input (by returning None from poll at least once). It was enough to make all tests fail. And applying fix fixed that.

[Tarrasch]

LGTM. But someone knowing pig should review.

[sceeter89]

Actually this issue has nothing to do with Pig itself, but if you know such a person it would be great to let her/him know.

[Tarrasch]

Okay. If nobody comments for a while I suppose this can be merged. 👍

[gpoulin]

LGTM, I would just change line 130 to temp_stdout = tempfile.TemporaryFile('wb') to make it explicit that the temporary file is expecting binary and not string.

[sceeter89]

@gpoulin Good point, thank you for that, I've just pushed this change.

[erikbern]

lgtm