How to extract data associated with attribute of XML file using python 3.2

Question

I have this xml format.....

<event timestamp="0.447463" bustype="LIN" channel="LIN 1">  
 <col name="Time"/>  
 <col name="Start of Frame">0.440708</col>  
 <col name="Channel">LIN 1</col>  
 <col name="Dir">Tx</col>  
 <col name="Event Type">LIN Frame (Diagnostic Request)</col>  
 <col name="Frame Name">MasterReq_DB</col>  
 <col name="Id">3C</col>  
 <col name="Data">81 06 04 04 FF FF 50 4C</col>  
 <col name="Publisher">TestMaster (simulated)</col>  
 <col name="Checksum">D3 &quot;Classic&quot;</col>  
 <col name="Header Duration">2.090 ms (40.1 bits)</col>  
 <col name="Resp. Duration">4.688 ms (90.0 bits)</col>  
 <col name="Time difference">0.049987</col>  
 <empty/>  
</event>

In above xml, i need to extract data associated with attribute 'name'
Am able to get all names but am unable to fetch >MasterReq_DB< field
Please help me ...
Thanks in advance

My python code is...

import sys 
import array
import string
from xml.dom.minidom import parse,parseString
from xml.dom import minidom                                              
input_file = open("test_input.txt",'r')                                                
alines = input_file.read()
word_lst = alines.split("'")
filename = word_lst[1]
pathname=word_lst[3]                                               
f = open(pathname,'r')
doc = minidom.parse(f)
node = doc.documentElement
events = doc.getElementsByTagName('event')
for event in events:
    #print (event)
    columns =  event.getElementsByTagName('col')
    for column in columns:
        #print (column)
        head = column.getAttribute('name')
        if (head == ('Frame Name')):
           print (head)
           request = head.firstChild.wholeText
           print (request)
print ("DOne")

What code have you tried? Have you looked at elementtree and lxml (the latter being a more powerful extension overlapping in functionality with the former). — Martijn Pieters
– Martijn Pieters, Commented Jun 16, 2012 at 9:14
And print (request) outputs what exactly? Have you tried print (repr(request))? I'd strongly advise switching to elementtree as a vastly superior XML API for python. — Martijn Pieters
– Martijn Pieters, Commented Jun 16, 2012 at 9:36
i get error as: Frame Name Traceback (most recent call last): File "C:\Users\rshirurm\Desktop\AD7180_aut\AD7180_auto.py", line 25, in <module> request = head.firstChild.wholeText AttributeError: 'str' object has no attribute 'firstChild' — Rohit
– Rohit, Commented Jun 16, 2012 at 9:51
There is your hint: head is a string (the value of the column attribute).. use column.firstChild perhaps? :-P — Martijn Pieters
– Martijn Pieters, Commented Jun 16, 2012 at 9:54

Lev Levitsky · Accepted Answer · 2012-06-16 09:58:34Z

1

Here's a primer to get you started with lxml if you wish to:

In [1]: x = '''<event timestamp="0.447463" bustype="LIN" channel="LIN 1">  
   ...:  <col name="Time"/>  
   ...:  <col name="Start of Frame">0.440708</col>  
   ...:  <col name="Channel">LIN 1</col>  
   ...:  <col name="Dir">Tx</col>  
   ...:  <col name="Event Type">LIN Frame (Diagnostic Request)</col>  
   ...:  <col name="Frame Name">MasterReq_DB</col>  
   ...:  <col name="Id">3C</col>  
   ...:  <col name="Data">81 06 04 04 FF FF 50 4C</col>  
   ...:  <col name="Publisher">TestMaster (simulated)</col>  
   ...:  <col name="Checksum">D3 &quot;Classic&quot;</col>  
   ...:  <col name="Header Duration">2.090 ms (40.1 bits)</col>  
   ...:  <col name="Resp. Duration">4.688 ms (90.0 bits)</col>  
   ...:  <col name="Time difference">0.049987</col>  
   ...:  <empty/>  
   ...: </event> '''

In [2]: from lxml import etree

In [3]: tree = etree.fromstring(x)

In [4]: [elem.text for elem in tree.xpath('//*[@name]')]
Out[4]: 
[None,
 '0.440708',
 'LIN 1',
 'Tx',
 'LIN Frame (Diagnostic Request)',
 'MasterReq_DB',
 '3C',
 '81 06 04 04 FF FF 50 4C',
 'TestMaster (simulated)',
 'D3 "Classic"',
 '2.090 ms (40.1 bits)',
 '4.688 ms (90.0 bits)',
 '0.049987']

In [5]: [name for name in tree.xpath('//@name')]
Out[5]: 
['Time',
 'Start of Frame',
 'Channel',
 'Dir',
 'Event Type',
 'Frame Name',
 'Id',
 'Data',
 'Publisher',
 'Checksum',
 'Header Duration',
 'Resp. Duration',
 'Time difference']

To read from file instead of a string, use lxml.etree.parse function.

Here's a link to lxml tutorial. This one is a reference for XPath syntax.

answered Jun 16, 2012 at 9:58

Lev Levitsky

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4 Comments

Rohit Over a year ago

hey,what do you suggest me ? use lxml or DOM bcos this is just start of my work and i need parse xml files which are in Mbytes...

Lev Levitsky Over a year ago

I haven't got any experience with DOM at all, to be honest. lxml is quite good for parsing. For parsing files of several Gb in size I use the iterparse method of lxml, works great. For smaller files something like the example in my answer is what I normally do.

Rohit Over a year ago

thanks for suggetion...How can i write output to excel2007...?

Lev Levitsky Over a year ago

@Rohit Take a look at this question.

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