Python字典键添加前缀的最有效方法

Question

我需要给Python字典添加前缀。

基本上，我希望用户在实例化字典时能够添加前缀，这样字典就会保存前缀，并且每次添加新键时都会将前缀添加到键的前面。但是，如果没有提供或更改前缀，则还要修改字典，这意味着旧字典键需要在保留其各自值的同时加上前缀。

使用情况：

我正在完成MWS API的最后一个API。 我根据每个调用需要具有特定参数的想法构建了API，例如：

def get_report(self, marketplaceids):
    # Here I process marketplaceids which is a python list
    # and send the following to Amazon:

    MarketplaceIdList.Id.1: 123,
    MarketplaceIdList.Id.2: 345,
    MarketplaceIdList.Id.3: 4343

    # By doing this I eliminate the complexity of the arguments Amazon expects

很不幸，最后两个API的实现比较困难，因为它们使用了亚马逊引入的一个名为“Datatypes”的新“特性”。

这些“Datatypes”是嵌套结构。例如：

我想从“InboundShipmentAPI”调用“CreateInboundShipment”操作，

该操作需要以下参数：

ShipmentId - String
InboundShipmentHeader - InboundShipmentHeader datatype
InboundShipmentItems - A list of InboundShipmentItem datatypes

问题发生的原因是InboundShipmentHeader是一个以另一种数据类型作为参数的数据类型。最终，亚马逊期望如下所示：

ShipmentId=102038383
InboundShipmentHeader.ShipmentName': 'somevalue',
InboundShipmentHeader.ShipFromAddress.Name': 'somevalue',
InboundShipmentHeader.ShipFromAddress.AddressLine1': 'somevalue',
InboundShipmentHeader.ShipFromAddress.City': 'somevalue',
InboundShipmentHeader.ShipFromAddress.StateOrProvinceCode': 'somevalue',
InboundShipmentHeader.ShipFromAddress.PostalCode': 'somevalue',
InboundShipmentHeader.ShipFromAddress.CountryCode': 'somevalue',
InboundShipmentHeader.DestinationFulfillmentCenterId': 'somevalue',
InboundShipmentHeader.ShipmentStatus': 'somevalue',
InboundShipmentHeader.LabelPrepPreference': 'somevalue',
InboundShipmentItems.member.1.QuantityShipped': 'somevalue',
InboundShipmentItems.member.2.QuantityShipped': 'somevalue',
InboundShipmentItems.member.1.SellerSKU': 'somevalue',
InboundShipmentItems.member.2.SellerSKU': 'somevalue',
InboundShipmentHeader.ShipFromAddress.AddressLine2': 'somevalue',
InboundShipmentHeader.ShipFromAddress.DistrictOrCounty': 'somevalue',

我希望能让人们更简单地进行调用，而不必担心每个参数的名称。

我的解决方案是创建一个基础数据类型类并创建不同的数据类型作为类。

目前我已经实现了如下内容：

class AmazonDataType(dict):
    """
    Base for all Amazon datatypes.
    """

    def __init__(self, *args, **kwargs):
        self._prefix = kwargs.pop('prefix', '')
        self.update(*args, **kwargs)

    @property
    def prefix(self):
        return self._prefix

    @prefix.setter
    def prefix(self, value):
        self._prefix = value
        newdict = {'%s.%s' % (value, key): dictvalue for key, dictvalue in self.iteritems()}
        self.clear()
        dict.update(self, newdict)

    def __setitem__(self, key, value):
        try:
            original_key = self.fields[key]
        except KeyError, e:
            raise e
        if isinstance(value, AmazonDataType):
            value.prefix = original_key
            dict.update(self, value)
        else:
            newkey = self.prefix + original_key if self.prefix else original_key
            dict.__setitem__(self, newkey, value)

    def update(self, *args, **kwargs):
        """
        Props to Matt Anderson (https://dev59.com/mXE95IYBdhLWcg3wPrkI#2390997)
        """
        for k, v in dict(*args, **kwargs).iteritems():
            self[k] = v


class InboundShipmentHeader(AmazonDataType):
    fields = {
        'name': 'ShipmentName',
        'address': 'ShipFromAddress',
        'fulfillment_center_id': 'DestinationFulfillmentCenterId',
        'label_preference': 'LabelPrepPreference',
        'cases_required': 'AreCasesRequired',
        'shipment_status': 'ShipmentStatus',
    }

那么，如果不是做

somedict = {
    'InboundShipmentHeader.ShipmentName': 'somevalue',
    'InboundShipmentHeader.ShipFromAddress.Name': 'somevalue',
    'InboundShipmentHeader.ShipFromAddress.AddressLine1': 'somevalue',
    'InboundShipmentHeader.ShipFromAddress.City': 'somevalue',
    'InboundShipmentHeader.ShipFromAddress.StateOrProvinceCode': 'somevalue',
    'InboundShipmentHeader.ShipFromAddress.PostalCode': 'somevalue',
    'InboundShipmentHeader.ShipFromAddress.CountryCode': 'somevalue',
    'InboundShipmentHeader.DestinationFulfillmentCenterId': 'somevalue',
    'InboundShipmentHeader.ShipmentStatus': 'somevalue',
    'InboundShipmentHeader.LabelPrepPreference': 'somevalue',
}

call_amazon(somedict)

我希望传递一些类似的东西

ShipmentHeader = InboundShipmentHeader()
ShipmentHeader['name'] = 'somevalue'
ShipmentHeader['address'] = address_datatype_instance
ShipmentHeader['fulfillment_center_id'] = 'somevalue'
ShipmentHeader['label_preference'] = 'somevalue'
ShipmentHeader['cases_required'] = 'somevalue'
ShipmentHeader['shipment_status'] = 'somevalue'

call_amazon(ShipmentHeader, otherparams)

在后台，call_amazon 方法执行以下操作：

ShipmentHeader.prefix = InboundShipmentHeader

- Paulo

---

你难道不需要在添加新前缀之前删除旧前缀吗？ - interjay

在前缀的setter中，我清空了字典并用新值替换了_prefix的值。 - Paulo

但是，你的字典键将会同时包含旧前缀和新前缀。 - interjay

只是出于好奇，你为什么需要这样做？ - Blender

@Aya的问题已更新... - Paulo

Answer 1

您可以子类化dict并添加一个方法（我不确定该如何称呼它，所以我们称其为dict）：

class AmazonDataType(dict):
    """
    Base for all Amazon datatypes.
    """

    def __init__(self, *args, **kwargs):
        self._prefix = kwargs.pop('prefix', self.__class__.__name__)

        super(AmazonDataType, self).__init__(*args, **kwargs)

    def __getattr__(self, key):
        return self.__getitem__(key)

    def __setattr__(self, key, value):
        return self.__setitem__(key, value)

    def dict(self):
        result = {}

        for key, value in self.items():
            if key.startswith('_'):
                continue

            key = self.fields.get(key, key)

            if isinstance(value, AmazonDataType):
                for skey, svalue in value.dict().items():
                    result['%s.%s' % (self._prefix, skey)] = svalue
            else:
                result['%s.%s' % (self._prefix, key)] = value

        return result

现在，这个接口更符合Python的规范：

class InboundShipmentHeader(AmazonDataType):
    fields = {
        'name': 'ShipmentName',
        'address': 'ShipFromAddress',
        'fulfillment_center_id': 'DestinationFulfillmentCenterId',
        'label_preference': 'LabelPrepPreference',
        'cases_required': 'AreCasesRequired',
        'shipment_status': 'ShipmentStatus',
    }

class Address(AmazonDataType):
    fields = {
        'name': 'Name',
        'address': 'AddressLine1',
        'city': 'City'
    }

address = Address(prefix='ShipFromAddress')
address.name = 'Foo'

header = InboundShipmentHeader()
header.name = 'somevalue'
header.address = address
header.fulfillment_center_id = 'somevalue'
header.label_preference = 'somevalue'
header.cases_required = 'somevalue'
header.shipment_status = 'somevalue'

header.dict() 的输出如下：

{'InboundShipmentHeader.AreCasesRequired': 'somevalue',
 'InboundShipmentHeader.DestinationFulfillmentCenterId': 'somevalue',
 'InboundShipmentHeader.LabelPrepPreference': 'somevalue',
 'InboundShipmentHeader.ShipFromAddress.Name': 'Foo',
 'InboundShipmentHeader.ShipmentName': 'somevalue',
 'InboundShipmentHeader.ShipmentStatus': 'somevalue'}

- Blender

Answer 2

看起来，你在抽象类中需要的翻译不仅仅是给字典键加前缀那么简单。

我会将翻译逻辑封装在一个基类中，并为每种类型创建子类，示例如下...

class AmazonDict(dict):
    translation_dict = {}

    def __init__(self, prefix):
        self.prefix = prefix

    def translate(self):
        result = {}
        for k, v in self.iteritems():
            if k not in self.translation_dict:
                continue
            if isinstance(v, AmazonDict):
                for sk, sv in v.translate().iteritems():
                    sk = '%s.%s' % (self.prefix, sk)
                    result[sk] = sv
            else:
                k = '%s.%s' % (self.prefix, self.translation_dict[k])
                result[k] = v
        return result


class ShipmentAddress(AmazonDict):
    translation_dict = {'name': 'Name',
                        'line1': 'AddressLine1'}


class ShipmentHeader(AmazonDict):
    translation_dict = {'name': 'ShipmentName',
                        'address': 'ShipFromAddress'}


address = ShipmentAddress('ShipFromAddress')
address['name'] = 'Fred Bloggs'
address['line1'] = '123 High Street'

header = ShipmentHeader('InboundShipmentHeader')
header['name'] = 'Something'
header['address'] = address

pprint.pprint(header.translate())

...它还处理子“对象”的递归，并输出...

{'InboundShipmentHeader.ShipFromAddress.AddressLine1': '123 High Street',
 'InboundShipmentHeader.ShipFromAddress.Name': 'Fred Bloggs',
 'InboundShipmentHeader.ShipmentName': 'Something'}

假设这是亚马逊期望的格式。

- Aya