Winreg import failure in appdirs

[zooba]

Environment

• pip version: 19.3.1
• Python version: 3.7.5 (modified)
• OS: Windows 10

The version of Python I am using is modified for security. Most importantly, ctypes is removed.

Description
Without ctypes available, appdirs will automatically use the _get_win_folder_from_registry function.

However, this function has not been updated for Python 3's winreg module - it tries/fails to import _winreg (the Python 2.x name).

Expected behavior

How to Reproduce

1. Rename DLLs\_ctypes.pyd to any other name, or move it elsewhere. (Or any other mechanism you like to prevent it from being imported)
2. Then run pip --version
3. An error occurs.

Output

(testenv) PS C:\testenv> pip --version
  File "C:\Python37_x64\lib\runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "C:\Python37_x64\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:\testenv\Scripts\pip.exe\__main__.py", line 5, in <module>
  File "c:\testenv\lib\site-packages\pip\_internal\main.py", line 13, in <module>
    from pip._internal.cli.autocompletion import autocomplete
  File "c:\testenv\lib\site-packages\pip\_internal\cli\autocompletion.py", line 11, in <module>
    from pip._internal.cli.main_parser import create_main_parser
  File "c:\testenv\lib\site-packages\pip\_internal\cli\main_parser.py", line 7, in <module>
    from pip._internal.cli import cmdoptions
  File "c:\testenv\lib\site-packages\pip\_internal\cli\cmdoptions.py", line 25, in <module>
    from pip._internal.locations import USER_CACHE_DIR, get_src_prefix
  File "c:\testenv\lib\site-packages\pip\_internal\locations.py", line 28, in <module>
    USER_CACHE_DIR = appdirs.user_cache_dir("pip")
  File "c:\testenv\lib\site-packages\pip\_internal\utils\appdirs.py", line 47, in user_cache_dir
    path = os.path.normpath(_get_win_folder("CSIDL_LOCAL_APPDATA"))
  File "c:\testenv\lib\site-packages\pip\_internal\utils\appdirs.py", line 207, in _get_win_folder_from_registry
    import _winreg
ModuleNotFoundError: No module named '_winreg'

[zooba]

Current code:

def _get_win_folder_from_registry(csidl_name):
    import _winreg

    shell_folder_name = {
        "CSIDL_APPDATA": "AppData",
        "CSIDL_COMMON_APPDATA": "Common AppData",
        "CSIDL_LOCAL_APPDATA": "Local AppData",
    }[csidl_name]

    key = _winreg.OpenKey(
        _winreg.HKEY_CURRENT_USER,
        r"Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders"
    )
    directory, _type = _winreg.QueryValueEx(key, shell_folder_name)
    return directory

Possible alternative:

def _get_win_folder_from_registry(csidl_name):
    return {
        "CSIDL_APPDATA": os.getenv("APPDATA"),
        "CSIDL_COMMON_APPDATA": os.getenv("PROGRAMDATA"),
        "CSIDL_LOCAL_APPDATA": os.getenv("LOCALAPPDATA"),
    }[csidl_name]

[zooba]

Alternatively, it looks like the 1.4.3 release uses slightly better handling of the imports to special-case PY3 (which personally I don't agree with - PY2 is the special case - but if you want to do the direct-vendor thing then simply updating should be okay for now).

[uranusjr]

Hmm, it looks pip 19.3.1 should already be using 1.4.3; something might be off here…

https://github.com/pypa/pip/blob/19.3.1/src/pip/_vendor/appdirs.py

It might be worthwhile to submit the environment variable method to upstream though. I’m kind of surprised appdirs doesn’t do that already.

[xavfernandez]

something might be off here…

Yup, cf #6040

[uranusjr]

I think #7501 also resolves this because the vendored appdirs uses the correct import.