Plugin for mypy to support zope interfaces
Plugin for mypy to support zope.interface
The goal is to be able to make zope interfaces to be treated as types in mypy sense.
Install both mypy and mypy-zope:
pip install mypy-zope
mypy.ini file in your project to enable the plugin:
[mypy] namespace_packages=True plugins=mypy_zope:plugin
You're done! You can now check your project with mypy:
What is supported?
You can browse sample files to get some sense on what features are supported and how they are handled.
You can define the interface and provide implementation:
class IAnimal(zope.interface.Interface): def say() -> None: pass @zope.interface.implementer(IAnimal) class Cow(object): def say(self) -> None: print("Moooo") animal: IAnimal = Cow() animal.say()
IAnimal will be treated as superclass of the implementation
Cow: you will be able to pass an implementation to functions accepting an
interface and all the usual polymorphism tricks.
It is also possible to declare the implementation using
function with the same effect as
@imlementer decorator. This is useful if
you do not control the code that defines the implementation class.
classImplements(Cow, IAnimal) animal: IAnimal = Cow()
Schema field type inference
A limited support for defining attributes as
zope.schema.Fields is supported too:
class IAnimal(zope.interface.Interface): number_of_legs = zope.schema.Int(title="Number of legs") @zope.interface.implementer(IAnimal) class Cow(object): number_of_legs = 4
In context of an interface, some known
zope.schema field types are
automatically translated to python types, so the
number_of_legs attributes is
getting the type
int in the example above. That means mypy will report an
error if you try to assign string to that attribute on an instance of
type. Custom fields or fields not recognized by plugin are given type
zope.schema.FieldProperty is limited, because type information is
not transferred from an interface to implementation attribute, but mypy doesn't
report errors on sources like this:
class IAnimal(zope.interface.Interface): number_of_legs = zope.schema.Int(title="Number of legs") @zope.interface.implementer(IAnimal) class Cow(object): number_of_legs = zope.schema.FieldProperty(IAnimal['number_of_legs'])
The type of
Cow.number_of_legs will become
Any in this case, even though
IAnimal.number_of_legs would be inferred as
Zope interfaces can be "called" to lookup an adapter, like this:
class IEUPowerSocket(zope.interface.Interface): def fit(): pass adapter = IEUPowerSocket(us_plug) adapter.fit()
Type of the
adapter variable will be set to
Conditional type inference
in an if statement,
mypy will know which type it is inside those statements.
if IAnimal.providedBy(ob): ob.number_of_legs += 2
Declaration of overloaded methods in interfaces
Similarly to regular overloaded
@overload declarations are supported in interfaces as well:
class IAnimal(zope.interface.Interface): @overload def say() -> str: ... @overload def say(count: int) -> List[str]: ... def say(count: int = None) -> Union[str, List[str]]: pass @zope.interface.implementer(IAnimal) class Cow(object): @overload def say(self) -> str: ... @overload def say(self, count: int) -> List[str]: ... def say(self, count: int = None) -> Union[str, List[str]]: if count is None: return "Mooo" return ["Mooo"] * count
Type stubs for zope.interface and zope.schema
mypy-zope ships with type stubs (
*.pyi files) for
zope.schema packages. They are enabled automatically as soon as plugin is
What is not supported?
zope.interface features are not supported:
- Declaring modules as interface implementers.
- Type inference for
- Stub files are largely incomplete
- Interface compatibility checker will not type-check non-method attributes
Currently the project is in a very early stage of development and might not be practically usable yet. Suggestions and pull requests are welcomed!
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