Discussion · bonfire.cafe

@clayote@peoplemaking.games · 3 months ago

I'm trying to add good #Python type annotations to #Lisien

Everything stored in it needs to be serializable in messagepack, so I've annotated all its function signatures with one of the type aliases

Key: TypeAlias = (
 str | int | float | None | tuple["Key", ...] | frozenset["Key"]
)
Value: TypeAlias = (
 Key
 | dict[Key, "Value"]
 | tuple["Value", ...]
 | list["Value"]
 | set["Value"]
 | frozenset["Value"]
)

Works ok so far.

But now I'm trying to use NewType to distinguish generic keys from those that name a Lisien entity, such as a node, edge, or graph.

You can't use NewType on type annotations, so I have to make a class for it. I did it like this:

clayote

@clayote@peoplemaking.games replied · 3 months ago

def is_valid_key(obj) -> TypeGuard[Key]:
 return (
 obj is None
 or isinstance(obj, (str, int, float))
 or (
 isinstance(obj, (tuple, frozenset))
 and all(is_valid_key(elem) for elem in obj)
 )
 )


class KeyClass:
 def __new__(cls, that: Key) -> Key:
 return that

 def __instancecheck__(self, instance) -> bool:
 return is_valid_key(instance)

Having to pick whether to use Key or KeyClass kinda sucks and I want to use just the class everywhere, but it seems like #PyCharm 's type checker can't tell that, when I annotate something KeyClass, that means it shouldn't complain when I pass in a string.

Is this a PyCharm limitation, or am I using types wrong?

clayote

@clayote@peoplemaking.games replied · 3 months ago

(note to self: actually run the code before you post it. just because it makes the type checker happy doesn't mean it runs)

clayote

@clayote@peoplemaking.games replied · 3 months ago

Well that's fairly bizarre. Seems like I have to do

_Key = str | int | float | None | tuple["_Key", ...] | frozenset["_Key"]
_KeyType = TypeVar("_KeyType", bound=_Key, covariant=True)


class Key(Generic[_KeyType]):
 def new(cls, obj: _Key) -> Key:
 if not is_valid_key(obj):
 raise TypeError("Invalid key")
 return obj

 def instancecheck(self, instance) -> bool:
 return is_valid_key(instance)

Even though instancecheck is alleged to be called to implement isinstance(obj, Key) it...isn't. Must be something about generics.

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