Question

我有我的xpath：

//*[namespace-uri() = 'http://foundation.org/UA/2011/03/NodeSet.xsd'][local-name() = 'Reference'][@ReferenceType = 'HasNotifier']/../../Description[@Locale="en"]

但不能使用此xml文件。也许是我的错，或者可能是一个lxml bug ...我不知道。我正在尝试几天来创建正确的xpath代码。但是unfurnetli，我不能这样做:(这是一个lxml错误还是我的错误？

我想得到的，如果“HasNotifier”打印“002CC-ESSO01。（WAAA05.01？1）”

我的XML文件示例：

<?xml version="1.0" encoding="UTF-8" ?>
<!-- created at 2017-03-09 08:23:40 -->
<UANodeSet xmlns="http://foundation.org/UA/2011/03/NodeSet.xsd" xmlns:uax="http://foundation.org/UA/2008/02/Types.xsd">
    <NamespaceUris>
        <Uri>http://www.vise.com/Server/UA/</Uri>
    </NamespaceUris>
    <Aliases>
        <!-- data types -->
        <Alias Alias="Boolean">i=1</Alias>
        <Alias Alias="SByte">i=2</Alias>
        <Alias Alias="Byte">i=3</Alias>
        <Alias Alias="Int16">i=4</Alias>
        <Alias Alias="UInt16">i=5</Alias>
        <Alias Alias="Int32">i=6</Alias>
        <Alias Alias="UInt32">i=7</Alias>
        <Alias Alias="Int64">i=8</Alias>
        <Alias Alias="UInt64">i=9</Alias>
        <Alias Alias="Float">i=10</Alias>
        <Alias Alias="Double">i=11</Alias>
        <Alias Alias="String">i=12</Alias>
        <Alias Alias="DateTime">i=13</Alias>
        <Alias Alias="ByteString">i=15</Alias>
        <Alias Alias="XmlElement">i=16</Alias>
        <Alias Alias="NodeId">i=17</Alias>
        <Alias Alias="LocalizedText">i=21</Alias>
        <!-- references -->
        <Alias Alias="Organizes">i=35</Alias>
        <Alias Alias="HasEventSource">i=36</Alias>
        <Alias Alias="HasModellingRule">i=37</Alias>
        <Alias Alias="HasTypeDefinition">i=40</Alias>
        <Alias Alias="HasSubtype">i=45</Alias>
        <Alias Alias="HasProperty">i=46</Alias>
        <Alias Alias="HasComponent">i=47</Alias>
        <Alias Alias="HasNotifier">i=48</Alias>
        <!-- types -->
        <Alias Alias="BaseDataType">i=24</Alias>
        <Alias Alias="BaseObjectType">i=58</Alias>
        <Alias Alias="FolderType">i=61</Alias>
        <Alias Alias="BaseVariableType">i=62</Alias>
        <Alias Alias="PropertyType">i=68</Alias>
        <!-- modelling rules -->
        <Alias Alias="New">i=78</Alias>
        <Alias Alias="Shared">i=79</Alias>
    </Aliases>
    <UAObject NodeId="ns=1;s=AGENT" BrowseName="1:AGENT">
        <DisplayName Locale="en">AGENT</DisplayName>
        <Description Locale="en">AGENT</Description>
        <References>
            <Reference ReferenceType="HasComponent" IsForward="false">i=85</Reference>
            <Reference ReferenceType="HasTypeDefinition">ns=1;s=ObjectTypes.VISE.Server.Local</Reference>
        </References>
        <Extensions>
            <VISE ExportedNodeId="ns=1;s=AGENT.OBJECTS.WAAA05.01.002CC-ESSO01" ExportedBrowseName="1:002CC-ESSO01" Upstream="true"/>
        </Extensions>
    </UAObject>
    <UAObject NodeId="ns=1;s=AGENT.OBJECTS" BrowseName="1:OBJECTS">
        <DisplayName Locale="en">OBJECTS</DisplayName>
        <Description Locale="en">OBJECTS</Description>
        <References>
            <Reference ReferenceType="HasComponent" IsForward="false">ns=1;s=AGENT</Reference>
            <Reference ReferenceType="HasTypeDefinition">FolderType</Reference>
        </References>
        <Extensions>
            <VISE Upstream="true"/>
        </Extensions>
    </UAObject>
    <UAObject NodeId="ns=1;s=AGENT.OBJECTS.WAAA05" BrowseName="1:WAAA05">
        <DisplayName Locale="en">WAAA05</DisplayName>
        <Description Locale="en">WAAA05</Description>
        <References>
            <Reference ReferenceType="HasComponent" IsForward="false">ns=1;s=AGENT.OBJECTS</Reference>
            <Reference ReferenceType="HasTypeDefinition">FolderType</Reference>
        </References>
        <Extensions>
            <VISE Upstream="true"/>
        </Extensions>
    </UAObject>
    <UAObject NodeId="ns=1;s=AGENT.OBJECTS.WAAA05.01" BrowseName="1:01">
        <DisplayName Locale="en">01</DisplayName>
        <Description Locale="en">01</Description>
        <References>
            <Reference ReferenceType="HasComponent" IsForward="false">ns=1;s=AGENT.OBJECTS.WAAA05</Reference>
            <Reference ReferenceType="HasTypeDefinition">FolderType</Reference>
        </References>
        <Extensions>
            <VISE Upstream="true"/>
        </Extensions>
    </UAObject>
    <UAObject NodeId="ns=1;s=AGENT.OBJECTS.WAAA05.01.002CC-ESSO01" BrowseName="1:002CC-ESSO01">
        <DisplayName Locale="en">002CC-ESSO01</DisplayName>
        <Description Locale="en">002CC-ESSO01</Description>
        <References>
            <Reference ReferenceType="HasComponent" IsForward="false">ns=1;s=AGENT.OBJECTS.WAAA05.01</Reference>
            <Reference ReferenceType="HasTypeDefinition">ns=1;s=ObjectTypes.PROJECT.Foren.Notek_Table</Reference>
            <Reference ReferenceType="HasComponent">ns=1;s=ObjectTypes.PROJECT.Foren.Notek_Table.Overview</Reference>
            <Reference ReferenceType="HasComponent">ns=1;s=ObjectTypes.PROJECT.Foren.Notek_Table.Version</Reference>
        </References>
    </UAObject>
    <UAVariable NodeId="ns=1;s=AGENT.OBJECTS.WAAA05.01.002CC-ESSO01.Pressed" BrowseName="1:Pressed" DataType="Boolean" AccessLevel="7" UserAccessLevel="7" Historizing="true">
        <DisplayName Locale="en">Pressed</DisplayName>
        <Description Locale="en">002CC-ESSO01.(WAAA05.01?1)</Description>
        <References>
            <Reference ReferenceType="HasComponent" IsForward="false">ns=1;s=AGENT.OBJECTS.WAAA05.01.002CC-ESSO01</Reference>
            <Reference ReferenceType="HasTypeDefinition">BaseVariableType</Reference>
            <Reference ReferenceType="HasNotifier">ns=1;s=ObjectTypes.PROJECT.Foren.Notek_Table.Pressed.ButtonPressed</Reference>
        </References>
        <Value>
            <uax:Boolean>false</uax:Boolean>
        </Value>
    </UAVariable>
    <UAVariable NodeId="ns=1;s=AGENT.OBJECTS.WAAA05.01.002CC-ESSO01.Pressed.MirrorInput" BrowseName="1:MirrorInput" DataType="String" AccessLevel="7" UserAccessLevel="7" Historizing="true">
        <DisplayName Locale="en">MirrorInput</DisplayName>
        <Description Locale="en">MirrorInput</Description>
        <References>
            <Reference ReferenceType="HasComponent" IsForward="false">ns=1;s=AGENT.OBJECTS.WAAA05.01.002CC-ESSO01.Pressed</Reference>
            <Reference ReferenceType="HasTypeDefinition">ns=1;s=VariableTypes.VISE.Mirror.Input</Reference>
        </References>
        <Value>
            <uax:String>Serwise/ns=4;s=Signals.WAAA05_01_002CC_ESSO01</uax:String>
        </Value>
    </UAVariable>
</UANodeSet>

Answer 1

这不是一个lxml错误。这是一个有效的XPath表达式：

//*[local-name() = 'Reference'][@ReferenceType = 'HasNotifier']/../../*[local-name() = 'Description'][@Locale='en']

您不需要namespace-uri() = ...，但必须使用*[local-name() = 'Description']而不是Description。

另一种方法是这样做。声明名称空间URI的前缀并在表达式中使用它：

from lxml import etree

NS = {'ns': 'http://foundation.org/UA/2011/03/NodeSet.xsd'}      
doc = etree.parse("nodeset.xml")
expr = "//ns:Reference[@ReferenceType = 'HasNotifier']/../../ns:Description[@Locale = 'en']"    
print(doc.xpath(expr, namespaces=NS)[0].text)

输出：

002CC-ESSO01.(WAAA05.01?1)

它是一个xpath（lxml）错误吗？

1 个答案: