Python driver - get_field is not implemented

[neumino]

We need get_field in some cases like #1434

cursor = r.db('cakemeter').table('stars') \
    .filter({"repo": "rethinkdb"}) \
    .get_field("stars") \
    .run()

Throws

AttributeError: 'Filter' object has no attribute 'get_field'

Users can use __getitem__ though.

[mlucy]

This seems like a bug to me: you sometimes need to use get_field rather than [] (e.g. if writing r('foo').do(lambda x: obj.get_field(x))).

Moving to 1.11.x and assigning to @Tryneus .

[Tryneus]

Fix up in review 1196. It also occurs to me the the python driver does not preserve the 'get_field' call in backtraces, and replaces it with brackets instead, which would result in an erroneous query in the example @mlucy gave, so I'll work on that as well.

[Tryneus]

The fix for the backtraces is up in review 1198.

[Tryneus]

This has been approved and merged into next in commits ac9b7fc and 2a5bbe3. The get_field change has been cherry-picked into v1.11.x in commit 8062708, but the backtrace fix had a merge conflict so I haven't cherry-picked it.