Enthought traits.api traitlist（）似乎支持item_validator

Question

在某些应用中，我发现 inthought traits.api 支持Python中的静态变量类型。

我正在尝试使用 item_validator关键字，但是使用item_validator关键字引发了一个错误...我尝试了此问题...

from traits.api import HasTraits, HasRequiredTraits, TraitList, TraitError
from traits.api import Regex, Enum

def garage_item_validator(item):
    """Validate item adjectives and reject pink or floral items"""
    try:
        if isinstance(item, Tool):
            if item.adjective!="pink" or item.adjective!="floral":
                return item
            else:
                raise ValueError()
    except ValueError():
        raise TraitError(f"Cannot put {item} in the Garage()")

class Tool(HasRequiredTraits):
    name = Regex(regex=r"[Ww]rench|[Ll]awnmower", required=True)
    adjective = Enum(*["brown", "rusty", "pink", "floral"], required=True)

    def __init__(self, name, adjective):
        self.name = name
        self.adjective = adjective

    def __repr__(self):
        return """<Tool: {}>""".format(self.name)

class Garage(HasTraits):
    things = TraitList(Tool, item_validator=garage_item_validator)  # <---- TraitList() doesn't work

    def __init__(self):
        self.things = list()

if __name__=="__main__":
    my_garage = Garage()
    my_garage.things.append(Tool("Lawnmower", "brown"))
    my_garage.things.append(Tool("wrench", "pink"))
    print(my_garage)

type> type> typeerror：__init_________init__ （）获得了一个意外的关键字参数'item_validator'，尽管特征清单文档明确表示item_validator受支持。

我还尝试使用 traits.api code> code> list list（） /a>，但它只是默默地忽略item_validator关键字。

我应该用什么来验证特征列表的内容？

Answer 1

TraitList 不是 Trait，而是执行验证和触发事件的 list 的子类。它由 List 特征在内部使用：

>>> from traits.api import HasStrictTraits, List, Int
>>> class Example(HasStrictTraits):
...     x = List(Int) 
... 
>>> example = Example()
>>> example.x
[]
>>> type(example.x)
<class 'traits.trait_list_object.TraitListObject'>
>>> type(example.x).mro()
[<class 'traits.trait_list_object.TraitListObject'>, <class 'traits.trait_list_object.TraitList'>, <class 'list'>, <class 'object'>]

并且它获取由 List 特征设置的 item_validator：

>>> example.x.item_validator
<bound method TraitListObject._item_validator of []>

因此，尽管没有钩子可以更改此设置验证器，它确实使用来自 Trait 的验证器，用作 List 的 trait 参数（在上面的示例中为 Int，因此列表只会保存整数项）。

>>> example.x.append("five")
Traceback (most recent call last):
...
traits.trait_errors.TraitError: Each element of the 'x' trait of an Example instance must be an integer, but a value of 'five' <class 'str'> was specified.

因此，您可以通过编写验证您想要的方式的自定义特征来实现您的目标。

在您的示例中，您希望这些项目是具有形容词某些属性的 Tool 实例，因此 Instance 特征是一个很好的起点：

from traits.api import BaseInstance, HasTraits, List

class GarageTool(BaseInstance):
    
    def __init__(self, **metadata):
        super().__init__(klass=Tool, allow_none=False, **metadata)
        
    def validate(self, object, name, value):
        # validate it is an instance of Tool
        value = super().validate(object, name, value)
        if value.adjective in {"pink", "floral"}:
            self.error(object, name, value)
        return value
    
    def info(self):
        # give better error messages
        return "a Tool which is neither pink nor floral"

class Garage(HasTraits):
    things = List(GarageTool())
    
if __name__ == "__main__":
    my_garage = Garage()
    my_garage.things.append(Tool("Lawnmower", "brown"))

    # now, pink correctly fails in garage_item_validator()
    my_garage.things.append(Tool("wrench", "pink")) # <-- pink fails

它会根据需要给出错误：

TraitError: Each element of the 'things' trait of a Garage instance must be a Tool which is neither pink nor floral, but a value of <__main__.Tool object at 0x7f899ad89830> <class '__main__.Tool'> was specified.

Answer 2

我在以前的尝试中犯了一个错误...

这是错误的... 工具应该是tool（） ...

class Garage(HasTraits):
    things = TraitList(Tool, item_validator=garage_item_validator)

这是正确的...

class Garage(HasTraits):
    things = TraitList(Tool(), item_validator=garage_item_validator)

此外，我发现我可以手动分配self.things.item_validator初始化garage（）

这也正确运行...

from traits.api import HasTraits, HasRequiredTraits, TraitList, TraitError
from traits.api import Regex, List, Enum, Either

def garage_item_validator(item):
    try:
        if isinstance(item, Tool):
            if item.adjective!="pink" and item.adjective!="floral":
                return item
            else:
                raise ValueError(item.adjective, item.name)
        else:
            raise ValueError(item.adjective, item.name)
    except Exception:
        raise ValueError(item.adjective, item.name)

class Tool(HasRequiredTraits):
    name = Regex(regex=r"[Ww]rench|[Ll]awnmower", required=True)
    adjective = Enum(*["brown", "rusty", "pink", "floral"])

    def __init__(self, name=None, adjective=None):
        self.name = name
        self.adjective = adjective

    def __repr__(self):
        return """<Tool: {}>""".format(self.name)

class Garage(HasTraits):
    things = TraitList(Tool())

    def __init__(self):
        self.things = list()
        self.things.item_validator = garage_item_validator
    #   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    #   Manually assign item_validator attr **after initializing self.things**

if __name__=="__main__":
    my_garage = Garage()
    my_garage.things.append(Tool("Lawnmower", "brown"))

    # now, pink correctly fails in garage_item_validator()
    my_garage.things.append(Tool("wrench", "pink")) # <-- pink fails

    print(my_garage)