xpath-expression 适用于文字但不适用于变量 [英] xpath-expression works with literal but not with variable
问题描述
我有一个包含如下数据的 XML 文件:
I have an XML file containing data looking as follows:
<?xml version="1.0" encoding="UTF-8"?>
<document date="2021-03-01" name="dataExport">
<CASHFLOW CASHFLOW_ID="001" C001="06-08"/><CASHFLOW_FIELD CASHFLOW_ID="001" C001="06-08" FIELDNAME="A001" VALUE="0"/><CASHFLOW_FIELD CASHFLOW_ID="001" F001="04-08-01" FIELDNAME="C254" VALUE="15.78"/>
<CASHFLOW CASHFLOW_ID="002" C001="06-08"/><CASHFLOW_FIELD CASHFLOW_ID="001" C001="06-08" FIELDNAME="A001" VALUE="2"/><CASHFLOW_FIELD CASHFLOW_ID="002" C001="06-08" FIELDNAME="C254" VALUE="10.55"/>
</document>
使用 XPath,我希望 - 对于每个条目 - 获取属性VALUE"的值;其中属性FIELDNAME"具有值C254".
Using XPath, I want - for each entry - to get the value of attribute "VALUE" where attribute "FIELDNAME" has value "C254".
我尝试了以下方法来实现我的目标(使用 python 库 lxml):
I tried the following to achieve my goal (using python library lxml):
import lxml.etree as etree
global tree
tree = etree.parse('filepath/filename.xml')
cashflow_ids = tree.xpath("//CASHFLOW/@CASHFLOW_ID")
for cashflow_id in cashflow_ids:
print(cashflow_id)
value_I_want = tree.xpath("//CASHFLOW_FIELD[@CASHFLOW_ID=cashflow_id and @FIELDNAME='C254']/@VALUE")
print(value_I_want)
不幸的是,使用此代码 value_I_want 在每种情况下都等于一个空列表.
Unfortunately, with this code value_I_want equals an empty list in each case.
问题在于变量cashflow_id".
The problem is the variable "cashflow_id".
如果我执行特定值的代码,它就可以工作.例如,以下工作正常:
If I execute the code for a specific value, it works. For example, the following works fine:
value_I_want = tree.xpath("//CASHFLOW_FIELD[@CASHFLOW_ID='002' and @FIELDNAME='C254']/@VALUE")
(在这种情况下,value_I_want 等于 10.55)
(value_I_want in this case equals 10.55)
如何使代码使用变量而不是文字?
How can I make the code work with a variable instead of a literal?
推荐答案
您正在传入字符串 cashflow_id
而您想要拥有值,将其转换为 f 字符串并传入变量 cashflow_id
像这样,它可以工作:
You're passing in the string cashflow_id
whereas you want to have the value, convert it to a f-string and pass in the variable cashflow_id
like this and it works:
value_I_want = tree.xpath(f"//CASHFLOW_FIELD[@CASHFLOW_ID={cashflow_id} and @FIELDNAME='C254']/@VALUE")
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