Replies: 4 comments 4 replies
-
Something like this maybe? A class variable is like an instance variable of a metaclass. Although different type checkers have different support for this. For pyright it works, for mypy generic metaclasses don't seem to work. |
Beta Was this translation helpful? Give feedback.
-
|
I'm getting |
Beta Was this translation helpful? Give feedback.
-
|
Interesting. I'm unable to reproduce that with pyright/pylance. I tried pyright latest version and code type checks fine for me. pyright playground also type checks fine. |
Beta Was this translation helpful? Give feedback.
-
|
Whenever you are expecting a subclass to provide something, using https://mypy-play.net/?mypy=latest&python=3.11&gist=617d24caceb1069f05fd252ca2fe97d2 As you can see an abstract property with a setter can be provided by a ClassVar, since it provides the same interface. It maybe obfuscates the intent a bit and is a lot of boilerplate for one attribute, but it does work. You may also wish to use the |
Beta Was this translation helpful? Give feedback.
-
|
Actually it looks like this doesn't enforce the property being defined in subclasses, although I'm not sure why. I'm certain I managed to get abstract properties to work this way in the past. |
Beta Was this translation helpful? Give feedback.
-
|
Alright, mypy will only emit an error if you try to create an instance of a subclass with abstract properties/methods that have not been implemented. It will automatically consider the class abstract, regardless of whether it's using So technically this will catch the error, just not at the definition site of the subclass, but only once you attempt to use the subclass: |
Beta Was this translation helpful? Give feedback.
-
|
Note that if you type ignore that error, mypy will still mostly do what you want: https://mypy-play.net/?mypy=latest&python=3.11&gist=fbe0cc42fcb250d60663d3e25567fa28 |
Beta Was this translation helpful? Give feedback.
-
|
The type check will be lost. |
Beta Was this translation helpful? Give feedback.
Uh oh!
There was an error while loading. Please reload this page.
-
I don't think this is standard terminology. There may be a better way of describing what I'm talking about.
I'm seeing that Python generics are instance-level generics - that is, each instance could have a different type for the type variable:
What I'm looking for is a way to specify that a subclass should specify a type that isn't specified by the base class.
Something like this:
Is there any way to specify this to people subclassing my class?
Assuming this example code does what I want it to do, and represents it in a way I want, how can I specify the typing?
Beta Was this translation helpful? Give feedback.
All reactions