### What changes were proposed in this pull request?
This PR aims to drop Python 2.7, 3.4 and 3.5.
Roughly speaking, it removes all the widely known Python 2 compatibility workarounds such as `sys.version` comparison, `__future__`. Also, it removes the Python 2 dedicated codes such as `ArrayConstructor` in Spark.
### Why are the changes needed?
1. Unsupport EOL Python versions
2. Reduce maintenance overhead and remove a bit of legacy codes and hacks for Python 2.
3. PyPy2 has a critical bug that causes a flaky test, SPARK-28358 given my testing and investigation.
4. Users can use Python type hints with Pandas UDFs without thinking about Python version
5. Users can leverage one latest cloudpickle, https://github.com/apache/spark/pull/28950. With Python 3.8+ it can also leverage C pickle.
### Does this PR introduce _any_ user-facing change?
Yes, users cannot use Python 2.7, 3.4 and 3.5 in the upcoming Spark version.
### How was this patch tested?
Manually tested and also tested in Jenkins.
Closes#28957 from HyukjinKwon/SPARK-32138.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
## What changes were proposed in this pull request?
Consistency in style, grammar and removal of extraneous characters.
## How was this patch tested?
Manually as this is a doc change.
Author: Shashwat Anand <me@shashwat.me>
Closes#20436 from ashashwat/SPARK-23174.
This patch improves our `dev/run-tests` script to test modules in a topologically-sorted order based on modules' dependencies. This will help to ensure that bugs in upstream projects are not misattributed to downstream projects because those projects' tests were the first ones to exhibit the failure
Topological sorting is also useful for shortening the feedback loop when testing pull requests: if I make a change in SQL then the SQL tests should run before MLlib, not after.
In addition, this patch also updates our test module definitions to split `sql` into `catalyst`, `sql`, and `hive` in order to allow more tests to be skipped when changing only `hive/` files.
Author: Josh Rosen <joshrosen@databricks.com>
Closes#10885 from JoshRosen/SPARK-8725.
