installation failed in python 3.8

[n3onUser]

1. require old cython version 0.14
   Actually, cython 0.29.17 is installed with python 3.8 and cython 0.14 failed to install with python 3.8

2. installation failed after with setup.py

$ python --version
Python 3.8.2
$ pip install poly2tri
Collecting poly2tri
  Using cached poly2tri-0.3.3.tar.gz (31 kB)
    ERROR: Command errored out with exit status 1:
     command: /vyv38/bin/python3.8 -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-4_9841_l/poly2tri/setup.py'"'"'; __file__='"'"'/tmp/pip-install-4_9841_l/poly2tri/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-install-4_9841_l/poly2tri/pip-egg-info
         cwd: /tmp/pip-install-4_9841_l/poly2tri/
    Complete output (5 lines):
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-install-4_9841_l/poly2tri/setup.py", line 8, in <module>
        m.Extension.__dict__ = m._Extension.__dict__
    AttributeError: attribute '__dict__' of 'type' objects is not writable
    ----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.