We started by introducing typevar, which is used to define a mutable type variable t. Then, with generic generics, we define a class called classa. In this class, we define two methods: methoda andmethod。In the methoda method, we annotate classa as the return value type. Since the classa class is a forward reference, it doesn't cause an error here.
InmethodIn the method, we use the type variable t as an annotation for the parameter type and the return value type. Since t is a mutable type variable, there will be no problem here either. We use forwardref to define forward references to classa classes. This way, we can use classa as a type annotation before defining a classa class. This section implements type annotations for classa classes and their methods by introducing features such as type variables, generics, and forward references, making them more legible and ensuring type correctness.
In Python, type annotations are just syntactic sugar and don't really affect how they run. So, at runtime,classaClasses don't__method__property, so an error will be reported.
To solve this problem, it needs to be usedtypingmoduleforwardrefgenerics to define a forward reference. Forward references allow us to refer to types that have not yet been defined in a type annotation.
Here's how to fix it:
from typing import forwardref, generic, typevar
t = typevar('t')
class classa(generic[t]):
def __init__(self) -none:
def __method__(self, v: t) -t:
classa = forwardref('classa')
class classa(generic[t]):
def __init__(self) -none:
def methoda(self) -classa:
return self
def __method__(self, v: classa) -classa:
In the ** above, we use firsttypevarA type variable is definedt。Then, we usegenericgenericsclassaKind. Inclassaclass, we define two methods:methodawith__method__
InmethodaMethods that we use:classaas a return value type. Due toclassaClasses are forward-referenced, so there will be no errors here.
In__method__Methods that we use:tas a parameter type and a return value type. Due totIt's a type variable, so there's no error here.
In the end, we useforwardrefto defineclassaForward reference to the class. In this way, inclassaclass definition, we can useclassaIt was annotated as a type.
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