Add a PEP661-compatible sentinels module
#37
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To add support for PEP661 we copy the reference implementation at https://github.com/taleinat/python-stdlib-sentinels. The code is copied verbatim from commit 9fdf9628d7bf010f0a66c72b717802c715c7d564, only adding the copyright notice, license and where we got the code from. Signed-off-by: Leandro Lucarella <[email protected]>
Also update the header to clarify now this is not a verbatim copy anymore and add another copyright line. Signed-off-by: Leandro Lucarella <[email protected]>
Signed-off-by: Leandro Lucarella <[email protected]>
We don't want to check implementation details that deal with multiple python implementations. We don't really want to *maintain* this code, we added it with the hope that it gets added to the Python standard library eventually. Signed-off-by: Leandro Lucarella <[email protected]>
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Signed-off-by: Leandro Lucarella <[email protected]>
Signed-off-by: Leandro Lucarella <[email protected]>
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Skipping release notes check as there is no release yet, we'll write the notes when the first release is out. |
Add missing docstrings and improve documentation to be compatible with mkdocstrings and Google style. Signed-off-by: Leandro Lucarella <[email protected]>
The PEP was updated in commit 410273e40bdbd1b58a63cebefdf8abcce6c620e3 but the reference implementation was not updated accordingly, so we apply the proposed change here and add a test for it too. Signed-off-by: Leandro Lucarella <[email protected]>
| if value is MISSING: | ||
| assert_type(value, MISSING) | ||
| else: | ||
| assert_type(value, int) |
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python3 example.py
Traceback (most recent call last):
File "/home/marenz/frequenz/frequenz-client-dispatch-python/example.py", line 8, in
def func(value: int | MISSING) -> None:
~~~~^~~~~~~~~
TypeError: unsupported operand type(s) for |: 'type' and 'Sentinel'
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Dammit. Reading the spec again, this might need some language support:
More formally, type checkers should recognize sentinel creations of the form NAME = Sentinel('NAME') as creating a new sentinel object. If the name passed to the Sentinel constructor does not match the name the object is assigned to, type checkers should emit an error.
Sentinels defined using this syntax may be used in type expressions. They represent a fully static type that has a single member, the sentinel object itself.
Type checkers should support narrowing union types involving sentinels using the is and is not operators:
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I tried several alternatives and couldn't make it work with a reasonable syntax, so I guess we need to wait for the official support. I tried other more old school implementations and they all suck, I guess the best approach for now is still to just do I think I will close for now. |
Introduce a new module for creating unique sentinel objects according to PEP661.
This is based in the reference implementation in https://github.com/taleinat/python-stdlib-sentinels (commit 410273e40bdbd1b58a63cebefdf8abcce6c620e3), and adapted to match this repository documentation standards and linting tools.