How to deal with enum compatibility errors

Causes and remedies for errors that occurred when installing Optuna

The environment is as follows

• Windows 10 Home
• python 3.6.5
• pip 19.3.1

I got an error when I ran the following code to install Optuna

Execution statement

pip install optuna

Execution result

Collecting optuna
  Downloading https://files.pythonhosted.org/packages/33/32/266d4afd269e3ecd7fcc595937c1733f65eae6c09c3caea74c0de0b88d78/optuna-1.5.0.tar.gz (200kB)
     |████████████████████████████████| 204kB 1.7MB/s
Collecting alembic
  Downloading https://files.pythonhosted.org/packages/60/1e/cabc75a189de0fbb2841d0975243e59bde8b7822bacbb95008ac6fe9ad47/alembic-1.4.2.tar.gz (1.1MB)
     |████████████████████████████████| 1.1MB 6.4MB/s
  Installing build dependencies ... error
  ERROR: Command errored out with exit status 1:
   command: 'D:\Users\(user_name)\Anaconda3\python.exe' 'D:\Users\(user_name)\Anaconda3\lib\site-packages\pip' install --ignore-installed --no-user --prefix 'C:\Users\(user_name)\AppData\Local\Temp\pip-build-env-5wsdb490\overlay' --no-warn-script-location --no-binary :none: --only-binary :none: -i https://pypi.org/simple -- 'setuptools>=40.8.0' wheel
       cwd: None
  Complete output (14 lines):
  Traceback (most recent call last):
    File "D:\Users\(user_name)\Anaconda3\lib\runpy.py", line 193, in _run_module_as_main
      "__main__", mod_spec)
    File "D:\Users\(user_name)\Anaconda3\lib\runpy.py", line 85, in _run_code
      exec(code, run_globals)
    File "D:\Users\(user_name)\Anaconda3\lib\site-packages\pip\__main__.py", line 16, in <module>
      from pip._internal.main import main as _main  # isort:skip # noqa
    File "D:\Users\(user_name)\Anaconda3\lib\site-packages\pip\_internal\main.py", line 8, in <module>
      import locale
    File "D:\Users\(user_name)\Anaconda3\lib\locale.py", line 16, in <module>
      import re
    File "D:\Users\(user_name)\Anaconda3\lib\re.py", line 142, in <module>
      class RegexFlag(enum.IntFlag):
  AttributeError: module 'enum' has no attribute 'IntFlag'
  ----------------------------------------
ERROR: Command errored out with exit status 1: 'D:\Users\(user_name)\Anaconda3\python.exe' 'D:\Users\(user_name)\Anaconda3\lib\site-packages\pip'
 install --ignore-installed --no-user --prefix 'C:\Users\(user_name)\AppData\Local\Temp\pip-build-env-5wsdb490\overlay' --no-warn-script-location 
--no-binary :none: --only-binary :none: -i https://pypi.org/simple -- 'setuptools>=40.8.0' wheel Check the logs for full command output.

error contents

Error statement

ERROR: Command errored out with exit status 1: 'D:\Users\(user_name)\Anaconda3\python.exe' 'D:\Users\(user_name)\Anaconda3\lib\site-packages\pip'
 install --ignore-installed --no-user --prefix 'C:\Users\(user_name)\AppData\Local\Temp\pip-build-env-5wsdb490\overlay' --no-warn-script-location 
--no-binary :none: --only-binary :none: -i https://pypi.org/simple -- 'setuptools>=40.8.0' wheel Check the logs for full command output.

Cause

The standard library enum module is used instead of the enum34 package, and since Python 3.6, the enum34 library is no longer compatible with the standard library enum.

solution

When using Python3.6 or later, the enum34 library is also unnecessary, so uninstall it and use the enum module of the standard library.

Uninstall enum34

pip uninstall enum34

After uninstalling enum34, I ran pip install optuna again and I was able to install Optuna safely!