Python 3.9 | Module 'ast' has no attribute 'NodeVisitor

[Ashlanfox]

I could not install ply for python 3.9 version but it works perfectly with previous versions (I'm using 3.8).
I ran the command on ubuntu: python3.9 -m pip install ply

Traceback (most recent call last):
File "/usr/lib/python3.9/runpy.py", line 197, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/usr/lib/python3.9/runpy.py", line 87, in _run_code
exec(code, run_globals)
File "/usr/lib/python3/dist-packages/pip/main.py", line 16, in
from pip._internal.cli.main import main as _main # isort:skip # noqa
File "/usr/lib/python3/dist-packages/pip/_internal/cli/main.py", line 10, in
from pip._internal.cli.autocompletion import autocomplete
File "/usr/lib/python3/dist-packages/pip/_internal/cli/autocompletion.py", line 9, in
from pip._internal.cli.main_parser import create_main_parser
File "/usr/lib/python3/dist-packages/pip/_internal/cli/main_parser.py", line 7, in
from pip._internal.cli import cmdoptions
File "/usr/lib/python3/dist-packages/pip/_internal/cli/cmdoptions.py", line 24, in
from pip._internal.exceptions import CommandError
File "/usr/lib/python3/dist-packages/pip/_internal/exceptions.py", line 10, in
from pip._vendor.six import iteritems
File "/usr/lib/python3/dist-packages/pip/_vendor/init.py", line 65, in
vendored("cachecontrol")
File "/usr/lib/python3/dist-packages/pip/_vendor/init.py", line 36, in vendored
import(modulename, globals(), locals(), level=0)
File "", line 1007, in _find_and_load
File "", line 986, in _find_and_load_unlocked
File "", line 664, in _load_unlocked
File "", line 627, in _load_backward_compatible
File "", line 259, in load_module
File "/usr/share/python-wheels/CacheControl-0.12.6-py2.py3-none-any.whl/cachecontrol/init.py", line 9, in
File "", line 1007, in _find_and_load
File "", line 986, in _find_and_load_unlocked
File "", line 664, in _load_unlocked
File "", line 627, in _load_backward_compatible
File "", line 259, in load_module
File "/usr/share/python-wheels/CacheControl-0.12.6-py2.py3-none-any.whl/cachecontrol/wrapper.py", line 1, in
File "", line 1007, in _find_and_load
File "", line 986, in _find_and_load_unlocked
File "", line 664, in _load_unlocked
File "", line 627, in _load_backward_compatible
File "", line 259, in load_module
File "/usr/share/python-wheels/CacheControl-0.12.6-py2.py3-none-any.whl/cachecontrol/adapter.py", line 5, in
File "", line 1007, in _find_and_load
File "", line 986, in _find_and_load_unlocked
File "", line 664, in _load_unlocked
File "", line 627, in _load_backward_compatible
File "", line 259, in load_module
File "/usr/share/python-wheels/requests-2.22.0-py2.py3-none-any.whl/requests/init.py", line 95, in
File "", line 1007, in _find_and_load
File "", line 986, in _find_and_load_unlocked
File "", line 664, in _load_unlocked
File "", line 627, in _load_backward_compatible
File "", line 259, in load_module
File "/usr/share/python-wheels/urllib3-1.25.8-py2.py3-none-any.whl/urllib3/contrib/pyopenssl.py", line 46, in
File "/usr/lib/python3/dist-packages/OpenSSL/init.py", line 8, in
from OpenSSL import crypto, SSL
File "/usr/lib/python3/dist-packages/OpenSSL/crypto.py", line 12, in
from cryptography import x509
File "/usr/lib/python3/dist-packages/cryptography/x509/init.py", line 8, in
from cryptography.x509.base import (
File "/usr/lib/python3/dist-packages/cryptography/x509/base.py", line 14, in
from cryptography import utils
File "/usr/lib/python3/dist-packages/cryptography/utils.py", line 9, in
import inspect
File "/usr/lib/python3.9/inspect.py", line 778, in
class _ClassFinder(ast.NodeVisitor):
AttributeError: module 'ast' has no attribute 'NodeVisitor'

[Ashlanfox]

This was a mistake on my side, I wrote a custom AST which I named ast.py and that broke the import on python 3.9. I simple renamed it to something else and it works again.

[Ioannis Filippidis]

If ast is a module within a Python package, then perhaps using absolute imports like from pkgname import ast as _ast would avoid shadowing the ast module from the Python standard library.

Another idea is to name the module _ast. Of course, this name would also hide the module, so it should not be used if the module includes functionality that is visible to package users. Especially for packages whose main purpose is to provide parsing infrastructure for some language, it is common that they make available the results of parsing as instances of AST classes from such a module. So in those cases the module needs to remain visible, and should not be named _ast.