The problem with adding a second None-like type is that gradually it
will acquire meaning as a possible value in some contexts. Maybe not in
your code, but in other people's. Then will there be a request for a
3rd such object? (4th, 5th ...?).
Defining your own sentinel object, as you do, seems like a good
solution. It means *you* control what meaning it has in the contexts
where it appears.
Best wishes
Rob Cliffe
On 07/06/2023 17:43, Dom Grigonis wrote:
This has been bugging me for a long time. It seems that python doesn’t
have a convention for “Undefined” type.
When I started using python I naturally used None for it (as advised).
However, the more I work with python, the more I find that None is a
meaningful type. And it is a type that is convenient to use in a lot
of cases, where it is not actually “None”.
One big example is:
numpy: array[None, :]
Another is simple cascading of defaults.
E.g.
```python
class A:
def __init__(self, default=’string'):
self.default = default
def method(self, default=None):
default = default if default is not None else self.default
dct[‘key’] = other_dict.get(‘key’, default)
return to_json(dct)
```
None has a logic in `some_func`, which is important.
Now if I want to enforce None passed to to_json I have no way to do it.
I know there are many workarounds for this, but there is no
`consistent` way of doing this.
I have been using Ellipsis in the past, but it doesn’t feel right,
because it also has a meaning and I might need to use those functions
with e.g. numpy in he future and will have to change it.
Now, I came back to this issue again and my latest solution is to just
define:
UNDEFINED = object()
in library constants.py
Then code above is very clear and I think this is a good and
sustainable solution.
I know, that in a way ’None’ is already this, but it is generally used
in 2 ways:
1. A variable/argument is undefined in python space
2. Global indication, that a value is undefined (e.g. equivalence of
null in json)
What I am proposing is to have 1 more constant in python ‘Undefined’,
which will indicate ‘Undefined’ in python space and leave None to be
used in more general sense.
I also found this article while looking for solution just now:
https://levelup.gitconnected.com/python-why-none-is-not-nothing-bb3de55dd471
It seems that people who use typing are also running into ambiguities
and trying to hack something together.
I avoid typing until its 99% mature so can't comment more on this.
What are your thoughts? Am I onto something or am I missing something?
Anyone else had similar encounters?
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