Stop building Pulsar Client for Python 2.7

[michaeljmarshall]

Motivation

We currently have several dependencies on Python 2.7. There is no need to build anything new for Python 2.7, as it has been deprecated for a while.

Modifications

• Remove the defunct homebrew script (the real one lives upstream).
• Update comments to indicate supported python languages.
• Update the python client build so that it only releases clients for python 3.x.

Verifying this change

I have manually run the scripts for these components to verify that the tests pass.

Does this pull request potentially affect one of the following parts:

Yes, this is a breaking change for the python 2.7 client. Given that python 2.7 is no longer supported, this is an acceptable breaking change.

Documentation

• doc

There are some minor doc updates as a part of this PR.

[michaeljmarshall]

I am having trouble with this test. I get the following error when running in a docker container on my laptop:

root@a89a873f16b0:/pulsar/pulsar-client-cpp# cd /pulsar/pulsar-client-cpp && cmake . $CMAKE_ARGS && make check-format && make -j8
-- ARCHITECTURE: x86_64
-- BUILD_DYNAMIC_LIB:  OFF
-- BUILD_STATIC_LIB:  ON
-- BUILD_TESTS:  ON
-- BUILD_PYTHON_WRAPPER:  ON
-- BUILD_WIRESHARK:  OFF
-- BUILD_PERF_TOOLS:  OFF
-- LINK_STATIC:  OFF
-- USE_LOG4CXX:  OFF
-- CMAKE_BUILD_TYPE:  Debug
-- Threads library: -pthread
Failed to find Protobuf in config mode, try to find it from system path
-- Protobuf_LIBRARIES: /usr/local/lib/libprotobuf.so
-- Protobuf_INCLUDE_DIRS: /usr/local/include
-- Found Boost: /usr/include (found version "1.58.0")  
-- Linking with Boost:System
-- Using std::regex
-- Found Boost: /usr/include (found version "1.58.0") found components: system 
-- PYTHON: 3.5.2
-- DETECTED Python 3
CMake Warning at /cmake-3.22.0-linux-x86_64/share/cmake-3.22/Modules/FindBoost.cmake:2201 (message):
  No header defined for python3-mt; skipping header check (note: header-only
  libraries have no designated component)
Call Stack (most recent call first):
  CMakeLists.txt:280 (find_package)


CMake Warning at /cmake-3.22.0-linux-x86_64/share/cmake-3.22/Modules/FindBoost.cmake:2201 (message):
  No header defined for python-py35; skipping header check (note: header-only
  libraries have no designated component)
Call Stack (most recent call first):
  CMakeLists.txt:280 (find_package)


CMake Warning at /cmake-3.22.0-linux-x86_64/share/cmake-3.22/Modules/FindBoost.cmake:2201 (message):
  No header defined for python-py35; skipping header check (note: header-only
  libraries have no designated component)
Call Stack (most recent call first):
  CMakeLists.txt:291 (find_package)


-- Found Boost: /usr/include (found version "1.58.0") found components: python-py35 
-- HAS_ZSTD: 1
-- HAS_SNAPPY: 1
-- Using Boost Python libs: 
CMake Error at python/CMakeLists.txt:84 (MESSAGE):
  Could not find Boost Python library


-- Configuring incomplete, errors occurred!
See also "/pulsar/pulsar-client-cpp/CMakeFiles/CMakeOutput.log".
See also "/pulsar/pulsar-client-cpp/CMakeFiles/CMakeError.log".

It is likely that apachepulsar/pulsar-build:ubuntu-16.04-pb3 does not have the correct dependencies.

[BewareMyPower]

I've tried to enable Python3 for CI some months ago, see #9684 and #8624. It's harder than I've thought.

It's right that the apachepulsar/pulsar-build:ubuntu-16.04-pb3 image doesn't have the Python3 support. We need to update the Dockerfile and add Boost Python3 dependency. But the most hard thing is the Python Functions incompatibility. It looks like Python Functions relies heavy on Python2.

[michaeljmarshall]

@BewareMyPower - thank you for the additional context!

[michaeljmarshall]

Superseded by #15185.