WIP/API: rename MultiIndex.labels to MultiIndex.codes
- [x] closes #13443
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

This PR renames ``MultiIndex.labels`` to ``MultiIndex.codes``.

This is a work in progress. Still need to do:
* go though the docs and doc strings, especially ``advanced.rst``
* Deprecation tests
* whatsnew section

Apart from the above this should be fairly complete, so would appreciate comments on the changes though.
Hello @topper-123! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`pandas/core/frame.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/core/frame.py) !

 - There are no PEP8 issues in the file [`pandas/core/groupby/generic.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/core/groupby/generic.py) !

 - There are no PEP8 issues in the file [`pandas/core/indexes/base.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/core/indexes/base.py) !

 - There are no PEP8 issues in the file [`pandas/core/indexes/multi.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/core/indexes/multi.py) !

 - There are no PEP8 issues in the file [`pandas/core/panel.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/core/panel.py) !

 - There are no PEP8 issues in the file [`pandas/core/reshape/concat.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/core/reshape/concat.py) !

 - There are no PEP8 issues in the file [`pandas/core/reshape/merge.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/core/reshape/merge.py) !

 - There are no PEP8 issues in the file [`pandas/core/reshape/reshape.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/core/reshape/reshape.py) !

 - There are no PEP8 issues in the file [`pandas/core/series.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/core/series.py) !

 - There are no PEP8 issues in the file [`pandas/core/util/hashing.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/core/util/hashing.py) !

 - There are no PEP8 issues in the file [`pandas/io/formats/excel.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/io/formats/excel.py) !

 - There are no PEP8 issues in the file [`pandas/io/pytables.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/io/pytables.py) !

 - There are no PEP8 issues in the file [`pandas/tests/frame/test_alter_axes.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/frame/test_alter_axes.py) !

 - There are no PEP8 issues in the file [`pandas/tests/groupby/test_groupby.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/groupby/test_groupby.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/multi/test_astype.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/indexes/multi/test_astype.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/multi/test_compat.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/indexes/multi/test_compat.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/multi/test_constructor.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/indexes/multi/test_constructor.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/multi/test_copy.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/indexes/multi/test_copy.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/multi/test_equivalence.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/indexes/multi/test_equivalence.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/multi/test_get_set.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/indexes/multi/test_get_set.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/multi/test_integrity.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/indexes/multi/test_integrity.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/multi/test_names.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/indexes/multi/test_names.py) !

 - There are no PEP8 issues in the file [`pandas/tests/test_multilevel.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/test_multilevel.py) !

 - There are no PEP8 issues in the file [`pandas/tests/test_panel.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/tests/test_panel.py) !

 - There are no PEP8 issues in the file [`pandas/util/testing.py`](https://github.com/topper-123/pandas/blob/38b241b0bef2f16d434cb4696fb8e7a0eaf63e35/pandas/util/testing.py) !



##### Comment last updated on November 13, 2018 at 08:57 Hours UTC Found some issues. Closed temporarily.