python lxml iterparse() 正在跳过第一个事件

Question

我正在使用 python lxml 中的 iterparse() 来解析大型 XML 文件并获取相关数据。这工作得很好，除了第一次发生事件。未捕获第一个节点的数据。当我想获取标签 "way" 时，也会发生同样的事情（不在此代码片段中）。 为什么第一个事件元素没有被捕获？

tree = etree.iterparse(state_file_xml, events=("start", "end"),tag=('node'))

context = iter(tree)

event, root = context.next()

nodes = {}
for event, elem in context:

    if ((event == 'end') and (elem.tag == 'node')) :
        id = elem.get("id")
        lat = float(elem.get("lat"))
        lon = float(elem.get("lon"))
        nodes[id] = [lat,lon]

我的 xml 文件如下所示：

<?xml version="1.0" encoding="UTF-8"?>
<osm version="0.6" generator="Overpass API 0.7.55.4 3079d8ea">
<note>The data included in this document is from www.openstreetmap.org. The data is made available under ODbL.</note>
<meta osm_base="2018-11-09T21:23:02Z"/>

  <way id="46916568">
      <nd ref="286427634"/>
      <nd ref="3371562694"/>
      <nd ref="3371562693"/>
      <nd ref="1044837456"/>
      <nd ref="1299487829"/>
      <nd ref="1299487860"/>
      <nd ref="284132018"/>
      <tag k="highway" v="secondary"/>
      <tag k="lit" v="yes"/>
      <tag k="maxspeed" v="50"/>
      <tag k="name" v="Zürcherstrasse"/>
      <tag k="surface" v="asphalt"/>
  </way>

  <node id="30228243" lat="47.4030908" lon="8.4049015"/>
  <node id="283533527" lat="47.4016971" lon="8.4036696"/>
  <node id="284132018" lat="47.4034413" lon="8.4042634"/>
  <node id="286427571" lat="47.4037481" lon="8.4058661"/>
  <node id="286427634" lat="47.4043045" lon="8.4032429"/>
  <node id="318217124" lat="47.4044289" lon="8.4054211"/>
  <node id="428076175" lat="47.4027948" lon="8.4045078"/>
  <node id="460527594" lat="47.4027445" lon="8.4055605"/>
  <node id="460527973" lat="47.4029993" lon="8.4040697"/>
  <node id="984783907" lat="47.4027808" lon="8.4054934"/>

Answer 1

context.next() 消费第一个节点：

In [14]: tree = etree.iterparse(state_file_xml, events=("start", "end"),tag=('node'))

In [15]: context = iter(tree)

In [16]: event, root = next(context)

In [17]: root.attrib
Out[17]: {'id': '30228243', 'lon': '8.4049015', 'lat': '47.4030908'}

（我将 context.next() 更改为 next(context) 以允许代码同时使用 Python2 和 Python3。）

顺便说一下，iterparse returns 是一个迭代器，所以 context = iter(tree) 是不必要的。由于您只需要处理每个 node 一次，因此 events=("end",) 就足够了：

import lxml.etree as ET

context = ET.iterparse(state_file_xml, events=("end",), tag=('node'))
nodes = {}

for event, elem in context:

    id = elem.get("id")
    lat = float(elem.get("lat"))
    lon = float(elem.get("lon"))
    nodes[id] = [lat,lon]

python lxml iterparse() 正在跳过第一个事件

python lxml iterparse() is skipping first event

events

lxml

python-2.7

iterparse