[Python] How do I prevent shelve module from appending ".db" to filename?

Python: 3.12.2, OS: MacOS 13.6.6

When I specify a filename to shelve.open, it appends .db to the filename:

% ls

% python
Python 3.12.2 (main, Feb 6 2024, 20:19:44) [Clang 15.0.0 (clang-1500.1.0.2.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import shelve
>>> with shelve.open("myfile"):
... pass
...
>>> quit()

% ls
myfile.db


Furthermore, if I attempt to open an existing file as "myfile.db" (with the extension), I get the following error:

% python
Python 3.12.2 (main, Feb 6 2024, 20:19:44) [Clang 15.0.0 (clang-1500.1.0.2.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import shelve
>>> with shelve.open("myfile.db"):
... pass
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/opt/homebrew/Cellar/python@3.12/3.12.2_1/Frameworks/Python.framework/Versions/3.12/lib/python3.12/shelve.py", line 243, in open
return DbfilenameShelf(filename, flag, protocol, writeback)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/Cellar/python@3.12/3.12.2_1/Frameworks/Python.framework/Versions/3.12/lib/python3.12/shelve.py", line 227, in __init__
Shelf.__init__(self, dbm.open(filename, flag), protocol, writeback)
^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/Cellar/python@3.12/3.12.2_1/Frameworks/Python.framework/Versions/3.12/lib/python3.12/dbm/__init__.py", line 89, in open
raise error[0]("db type could not be determined")
dbm.error: db type could not be determined


Opening the existing file as simply "myfile" with no extension works fine, however.

1. How do I prevent shelve.open from appending ".db" to the filename?
2. Why can't I open existing databases if I specify their ".db" extension?

Neither of these issues happen on Python 3.10.12 on Ubuntu 22, so I'm not sure if it's a Python version thing, or a platform thing.

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