每次调用 python 类时创建一个新副本

Question

我需要一些指导，了解如何正确设置它以完成我正在尝试做的事情。 我有一个名为属性块的类，然后我将使用它来创建 3 或 4 个属性块对象。如下图...

class AttributeBlock():
    def __init__(self, key, label, isClosed, isRequired, attributes):
        self.key = key
        self.label = label
        self.isClosed = isClosed
        self.isRequired = isRequired
        self.attributes = attributes if attributes is not None else {}

3 属性块对象

AttributeBlock(
    key="Sphere",
    isRequired=True,
    attributes=[
        ''' Other class objects '''
        BoolProperty("ishidden", False, "Hidden"),
    ]
)

AttributeBlock(
    key="Box",
    isRequired=True,
    attributes=[
        ''' Other class objects '''
        BoolProperty("ishidden", True, "Hidden"),
    ]
)

AttributeBlock(
    key="Circle",
    isRequired=False,
    attributes=[
        ''' Other class objects '''
        BoolProperty("ishidden", True, "Hidden"),
    ]
)

然后我想要做的是能够将这些 AttributeBlocks 之一添加到一个对象中，确保在添加它时，它是 AttributeBlock 的一个新实例，因此它的子属性对象是新实例。

这是我将添加属性块的对象。

class ToyBox():
    def __init__(self, name="", attributes=[]):
        self.name = name
        self.attributes = attributes[:]

newToyBox = ToyBox()
newToyBox.name = "Jimmy"

伪代码

def add_attribute_block(toybox = None, key = "" ):
    if an AttributeBlock with the matching key exists:
        add it to toybox.attributes

add_attribute_block( newToyBox, "Box" )

print newToyBox
>>
ToyBox
name="Jimmy"
attributes=[
    AttributeBlock(
        key="Box",
        isRequired=True,
        attributes=[
            BoolProperty("ishidden", True, "Hidden"),
        ]
    ),
    AttributeBlock(
        key="Sphere",
        isRequired=True,
        attributes=[
            BoolProperty("ishidden", True, "Hidden"),
        ]
    )
]

Answer 1

如果您想自动跟踪所有创建的AttributeBlockobjects，您可以使用类属性：

class AttributeBlock():
    objects = []
    def __init__(self, key, label, isClosed, isRequired, attributes):
        self.key = key
        self.label = label
        self.isClosed = isClosed
        self.isRequired = isRequired
        self.attributes = attributes if attributes is not None else {}
        self.objects.append(self)

完成此操作后，add_attribute 可能变为：

def add_attribute_block(toybox = None, key = "" ):
    if toybox is not None:
        for obj in AttributeBlock.objects:
            if obj.key == key:
                toybox.attributes.append(obj)
                break

您也可以为类属性使用映射而不是列表：

class AttributeBlock():
    objects = {]
    def __init__(self, key, label, isClosed, isRequired, attributes):
        if key in self.objects:
            # raise a custom exception
        ...
        self.objects[key] = self

那么你可以简单地使用：

def add_attribute_block(toybox = None, key = "" ):
    if toybox is not None:
        if key in AttributeBlock.objects:
            toybox.attributes.append(AttributeBlock.objects[key])

如果要将列表对象的副本放入ToyBox，则必须更改创建方法以允许不将该副本放入全局列表中。在这种情况下，代码将变为：

class AttributeBlock():
    objects = {}
    dummy = {}
    def __init__(self, key, label, isClosed, isRequired,
             attributes, glob = None):
        if glob is None:
            glob = self.objects
        if key in glob:
            raise ValueError(str(key) + " already exists")
        self.key = key
        self.label = label
        self.isClosed = isClosed
        self.isRequired = isRequired
        self.attributes = attributes if attributes is not None else {}
        if glob is not self.dummy:
            glob[key] = self
    def copy(self):
        return AttributeBlock(self.key, self.label, self.isClosed,
                      self.isRequired, self.attributes[:],
                      self.dummy)

带有一个允许不将新创建的对象存储在任何容器中的虚拟类对象，以及一个允许将其存储在外部字典中的可选glob 参数。还要注意精确使用dummy 的copy 方法。

add_attribute_block 变为：

def add_attribute_block(toybox = None, key = "", glob = None ):
    if glob is None:
        glob = AttributeBlock.objects
    if toybox is not None:
        if key in glob:
            toybox.attributes.append(AttributeBlock.objects[key].copy())

使用copy方法在ToyBox中存储一个未存储在全局容器中的原始对象的副本。

Answer 2

如果要确保添加到 ToyBox 的 Attribute 实例是副本，最简单的方法是使用 standard copy module

import copy
...
class ToyBox(object):
    ...
    def add_attribute(self, attribute):
        self.attributes.append(copy.deepcopy(attribute))

Answer 3

将所有属性块放在一个列表中。

blocks = []

// add your AttributeBlocks to this list
blocks.append(block1)
blocks.append(block2)
blocks.append(block3)

那么就简单了。

def add_attribute_block(toybox, key):
    #loop over list of blocks and find the block with that key
    for block in blocks:
        if block.key == key:
            #only add it to the toybox if its not already in there
            if not any(key in l.key for l in toybox.attributes):
                toybox.attributes.append(block)
                break

注意：

l.key for l in toybox.attributes 是一个列表推导，并为您提供所有键的列表。

如果key 在该列表中，则any(key in l.key for l in toybox.attributes) 返回True。

Answer 4

如果我理解正确，您希望每个 ToyBox 实例都包含一个 AttributeBlock 实例列表，使用 列表中还存在相同的名称。

class AttributeBlock():
    def __init__(self, key): # demo, add the other parameters/attrs
        self.key = key
    def __str__(self):
        return self.key # add the other parameters/attrs

class ToyBox(object):
    def __init__(self):
        self.attributes = []

    def add_attr(self, a):
        gen = (attr for attr in self.attributes if attr.key == a.key)
        try:
            next(gen)
        except StopIteration:
            self.attributes.append(a)

    def __str__(self):
        return ','.join(map(str,self.attributes))

所以现在我们可以做

>>> toy = ToyBox()
>>> toy.add_attr(AttributeBlock("Box"))
>>> toy.add_attr(AttributeBlock("Sphere"))
>>> toy.add_attr(AttributeBlock("Box"))
>>> print toy
Box,Sphere

如您所见，将add_attribute 函数设为ToyBox 的实例方法是有意义的

顺便说一句，如果attributes 列表中的对象数量很大，最好使用字典：

class ToyBox(object):
    def __init__(self):
        self.attributes = dict()

    def add_attr(self, a):
        if a.key not in self.attributes:
            self.attributes[a.key] = a

    def __str__(self):
        return ','.join(map(str,self.attributes.values()))

注意：如果您想保持添加对象的顺序，请改用OrderedDict