Parsing XML with Python and etree

Question

I want to extract all the way elements that contain a tag with the key 'highway' and a specific value from the following example Open Street Map XML file:

<?xml version="1.0" encoding="UTF-8"?>
<osm version="0.6" generator="CGImap 0.0.2">
 <bounds minlat="54.0889580" minlon="12.2487570" maxlat="54.0913900" maxlon="12.2524800"/>

 <node id="298884272" lat="54.0901447" lon="12.2516513" user="SvenHRO" uid="46882" visible="true" version="1" changeset="676636" timestamp="2008-09-21T21:37:45Z"/>
 <way id="26659127" user="Masch" uid="55988" visible="true" version="5" changeset="4142606" timestamp="2010-03-16T11:47:08Z">
  <nd ref="292403538"/>
  <nd ref="298884289"/>

  <nd ref="261728686"/>
  <tag k="highway" v="unclassified"/>
  <tag k="name" v="Pastower Straße"/>
 </way>
 <relation id="56688" user="kmvar" uid="56190" visible="true" version="28" changeset="6947637" timestamp="2011-01-12T14:23:49Z">
  <member type="node" ref="294942404" role=""/>
  ...
  <member type="node" ref="364933006" role=""/>
  <member type="way" ref="4579143" role=""/>
  ...
  <member type="node" ref="249673494" role=""/>
  <tag k="name" v="Küstenbus Linie 123"/>
  <tag k="network" v="VVW"/>
  <tag k="operator" v="Regionalverkehr Küste"/>
  <tag k="ref" v="123"/>
  <tag k="route" v="bus"/>
  <tag k="type" v="route"/>
 </relation>

</osm>

To do this; I wrote the following piece of Python code that uses the Etree library. It parses the XML document and uses the findall function (with XPath syntax)

import xml.etree.ElementTree as ET
supported_highways = ('motorway', 'trunk', 'primary', 'secondary', 'tertiary', 'unclassified', 'residential', 'highway_link', 'trunk_link', 'primary_link', 'secondary_link', 'tertiary_link')

class OSMParser:

    def __init__(self, inputData):
        self.root = ET.fromstring(inputData)


    def getRoads(self):
        ways = dict()
        for road in self.root.findall('./way/'):
            highway_tags = road.findall("./tag[@k='highway']")
            if not highway_tags:
                continue
            if all(highway.attrib['v'] not in supported_highways for highway in highway_tags):
                continue

However when I run the code, it does not find tag of the way element (the second findall produces an empty list). Any idea what's wrong? Thank you.

Just print root.tag and root.getchildren(). Check way tag is child of root tag or not. — Vivek Sable
– Vivek Sable, Commented Apr 20, 2015 at 8:24

user1907906 · Accepted Answer · 2015-04-20 08:09:48Z

1

Try the XPath //way/ instead of ./way/.

answered Apr 20, 2015 at 8:09

user1907906

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Comments

Vivek Sable · Accepted Answer · 2015-04-20 08:19:05Z

0

Its working.

>>> root.findall("./way/tag[@k='highway']")
[<Element 'tag' at 0xb74568ac>]

I think in your input content tag way is not child of main start tag i.e. root tag.

or use lxml.etree

>>> import lxml.etree as ET1
>>> root = ET1.fromstring(content)
>>> root.xpath("//way/tag[@k='highway']")
[<Element tag at 0xb745642c>]

answered Apr 20, 2015 at 8:19

Vivek Sable

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