如何使用Python添加不重复的XML元素

Question

使用Python提取元数据XML文件，从Python脚本填充各种元素，然后将XML文件保存回其源代码。有一个名为“citeinfo”的现有元素，我正在尝试在其中创建两个子元素，一个称为“pubdate”，另一个称为“othercit”。当我运行脚本时，我没有得到任何错误，但是当我打开XML后处理时，我得到了第二个“引文”元素组，它是“citeinfo”的父元素，并且是我所有新元素的一行。这是我的Python：

import arcpy, sys  
from xml.etree.ElementTree import ElementTree  
from xml.etree.ElementTree import Element, SubElement
import xml.etree.ElementTree as ET
from arcpy import env  
env.overwriteOutput = True  
fcpath         = r"...\HL Metadata to BR Sample Data.gdb\NCI20102014_Oral"
translatorpath = r"...\Translator\ARCGIS2FGDC.xml"
xmlfile        = r"...\Extras\FullMetaFC.xml"
arcpy.ExportMetadata_conversion(fcpath, translatorpath, xmlfile)

tree = ElementTree()
tree.parse(xmlfile)

a   = tree.find('idinfo')
aa  = tree.find('metainfo')
aaa = tree.find('eainfo')

b = ET.SubElement(a, 'citation')
c = ET.SubElement(b, 'citeinfo')
bb = ET.SubElement(c, 'pubdate')
d = ET.SubElement(c, 'othercit')
e = ET.SubElement(a, 'descript')
f = ET.SubElement(e, 'abstract')
g = ET.SubElement(e, 'purpose')

title       = tree.find("idinfo/citation/citeinfo/title")
public_date = tree.find("idinfo/citation/citeinfo/pubdate")
cit_source  = tree.find("idinfo/citation/citeinfo/othercit")
abstract    = tree.find("idinfo/descript/abstract")
purpose     = tree.find("idinfo/descript/purpose")

title.text       = "Oral Cancer Incidence by County"
bb.text = "99990088"
d.text  = "https://statecancerprofiles.cancer.gov/"
abstract.text    = "Incidence rates are..."
purpose.text     = "The State Cancer Profiles..."

tree.write(xmlfile)

arcpy.ImportMetadata_conversion(xmlfile, "FROM_FGDC", fcpath, "ENABLED")

以下是XML：

   <citation>
      <citeinfo>
        <origin>X</origin>
        <title>META_TESTING</title>
        <geoform>vector digital data</geoform>
      <pubdate>20102010</pubdate><othercit>www.google.com</othercit></citeinfo>
    </citation>

我希望“引文”组看起来像：

    <citation>
      <citeinfo>
        <title>National Cancer Institute, Oral Cancer Incidence by County</title>
        <geoform>vector digital data</geoform>
        <pubdate>20120510</pubdate>
        <othercit>www.google.com</othercit>
      </citeinfo>
    </citation>

Answer 1

我将创建一个小助手函数来确保元素的存在。如果它存在，它返回它-如果它不存在，它创建它。你知道吗

def ensure_elem(context, name):
    elem = context.find(name)
    return ET.SubElement(context, name) if elem is None else elem

现在你可以做：

tree = ET.parse(xmlfile)

# ensure we have a /metadata/idinfo/citation/citeinfo hierarchy
metadata = tree.getroot()
idinfo = ensure_elem(metadata, "idinfo")
citation = ensure_elem(idinfo, "citation")
citeinfo = ensure_elem(citation, "citeinfo")

# update the text of elements beneath citeinfo
ensure_elem(citeinfo, 'pubdate').text = "new pubdate"
ensure_elem(citeinfo, 'title').text = "new title"
# ...and so on

tree.write(xmlfile)

注意，您可以在一行代码中ET.parse()一个文件。你知道吗

---

简而言之，我们可以：

e = ensure_elem

# ensure we have a /metadata/idinfo/citation/citeinfo hierarchy
citeinfo = e(e(e(tree.getroot(), "idinfo"), "citation"), "citeinfo")

---

要漂亮地打印ElementTree文档，可以使用以下功能：

def indent(tree, indent_by='  '):
    irrelevant = lambda s: s is None or s.lstrip('\r\n\t\v ') == ''
    indent_str = lambda i: '\n' + indent_by * i

    def indent(elem, level=0, last_child=True):
        if len(elem) and irrelevant(elem.text):
            elem.text = indent_str(level+1)

        if irrelevant(elem.tail):
            elem.tail = indent_str(level-(1 if last_child else 0))

        for i, child in enumerate(elem, 1):
            indent(child, level+1, i==len(elem))

    indent(tree.getroot())