[issue47060] importlib.metadata.version can return None

[David Robertson]

New submission from David Robertson :

Originally written up at the typeshed repo: 
https://github.com/python/typeshed/issues/7513. The conclusion was that this is 
a bug in the implementation rather than an incorrect annotation.

To my surprise, I discovered in 
https://github.com/matrix-org/synapse/issues/12223 that it is possible for 
`importlib.metadata.version(...)` to return `None`. To reproduce this:

1. Create a new virtual environment. I'm using CPython 3.10.2 as my interpreter.
2. Within the venv, `pip install bottle`. (Any package will do; I choose 
`bottle` because it's small and doesn't have any dependencies).
3. Check importlib reports the `version` of `bottle`:
   ```python
   >>> import importlib.metadata as m
   >>> m.version('bottle')
   '0.12.19'
   ```
4. Here's the dirty bit: remove the metadata files for that package but keep 
the metadata directory.
   - Use `pip show bottle` to find the `site-packages` location
   - From there, remove all files in the `bottle-VERSION-.dist-info` directory: 
`rm /path/to/site-packages/bottle-VERSION.dist-info/*'.
5. The `version` of `bottle` is now judged to be `None`:
   ```python
   >>> import importlib.metadata as m
   >>> m.version("bottle") is None
   True
   ```
   `pip show bottle` now determines that `bottle` isn't installed:
   ```shell
   $ pip show bottle
   WARNING: Package(s) not found: bottle
   ```

As well as importlib.metadata.version, importlib.metadata.Distribution.version 
and importlib.metadata.Distribution.name return None in this situation.

I couldn't see any suggestion in the stdlib docs 
(https://docs.python.org/3.10/library/importlib.metadata.html#distribution-versions)
 that this was possible. (Aside: it'd be great if the docs mention that 
PackageNotFoundError is raised if a package is not installed.)

No-one in their right mind should do step 4 willingly, but I have seen it 
happen in the wild (https://github.com/matrix-org/synapse/issues/12223). We 
suspected a botched backup or similar was to blame.

I'm not familiar with all the machinery of Python package management, but I 
think I'd expect there to be a PackageNotFoundError raised in this situation? 
(I can imagine a package that doesn't declare its version, where `version()` 
returning `None` might make sense; but that feels odd.) Is the behaviour as 
intended?

It looks like this might be related to 
https://github.com/python/importlib_metadata/issues/371?

--
components: Library (Lib)
messages: 415516
nosy: David Robertson
priority: normal
severity: normal
status: open
title: importlib.metadata.version can return None
type: behavior
versions: Python 3.10

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[issue23057] [Windows] asyncio: support signal handlers on Windows (feature request)

[David Robertson]

David Robertson added the comment:

Dear all, I have just been trying to understand the TCP Echo example from the 
asyncio documentation:
https://docs.python.org/3/library/asyncio-protocol.html#protocol-examples
I copied the two examples from the docs into `server.py' and `client.py'. I ran 
server.py first and hit control-C. This did not close the server as expected. 
However, if I then ran client.py, the act of sending a message to the server 
seemed to prompt it to receive the KeyboardInterrupt and close! In turn this 
caused an OSError to be raised by the client.

Some searching lead me to StackOverflow and then to this bug. I wanted to point 
out this behaviour, as I didn't see it mentioned in any of the previous 
comments. Plus, I thought it was a shame that the first example I looked didn't 
behave as described!

I'm curently running Python 3.3.1 on Windows 7 and I'm using asyncio 3.4.3 from 
PyPI.

--
nosy: +David Robertson

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