Reading an XML file and printing specific fields using the Python language

Question

I have the following XML file (actually it’s just a piece of the file):

<!DOCTYPE sysstat PUBLIC "DTD v2.19 sysstat //EN"
        "http://pagesperso-orange.fr/sebastien.godard/sysstat-2.19.dtd">
        <sysstat>
            <sysdata-version>2.19</sysdata-version>
            <host nodename="ServerLabDoS">
                <sysname>Linux</sysname>
                <release>3.16.0-4-686-pae</release>
                <machine>i686</machine>
                <number-of-cpus>1</number-of-cpus>
                <file-date>2017-04-10</file-date>
                <file-utc-time>10:39:04</file-utc-time>
                <statistics>
                    <timestamp date="2017-04-10" time="07:50:12" utc="0" interval="119">
                        <memory per="second" unit="kB">
                            <memfree>1140168</memfree>
                            <memused>131440</memused>
                            <memused-percent>10.34</memused-percent>
                            <buffers>10928</buffers>
                            <cached>51716</cached>
                            <commit>510544</commit>
                            <commit-percent>28.87</commit-percent>
                            <active>56880</active>
                            <inactive>29832</inactive>
                            <dirty>44</dirty>
                        </memory>
                        <network per="second">
                            <net-dev iface="lo" rxpck="0.00" txpck="0.00" rxkB="0.00" txkB="0.00" rxcmp="0.00" txcmp="0.00" rxmcst="0.00" ifutil-percent="0.00"/>
                            <net-dev iface="eth0" rxpck="12.58" txpck="11.50" rxkB="11.95" txkB="0.85" rxcmp="0.00" txcmp="0.00" rxmcst="0.00" ifutil-percent="0.00"/>
                        </network>
                    </timestamp>
                    <timestamp date="2017-04-10" time="07:52:01" utc="0" interval="107">
                        <memory per="second" unit="kB">
                            <memfree>1140444</memfree>
                            <memused>131164</memused>
                            <memused-percent>10.31</memused-percent>
                            <buffers>11288</buffers>
                            <cached>51932</cached>
                            <commit>509260</commit>
                            <commit-percent>28.80</commit-percent>
                            <active>57024</active>
                            <inactive>29840</inactive>
                            <dirty>28</dirty>
                        </memory>
                        <network per="second">
                            <net-dev iface="lo" rxpck="0.00" txpck="0.00" rxkB="0.00" txkB="0.00" rxcmp="0.00" txcmp="0.00" rxmcst="0.00" ifutil-percent="0.00"/>
                            <net-dev iface="eth0" rxpck="13.89" txpck="12.69" rxkB="13.71" txkB="0.93" rxcmp="0.00" txcmp="0.00" rxmcst="0.00" ifutil-percent="0.00"/>
                        </network>
                    </timestamp>
                    <timestamp date="2017-04-10" time="07:54:01" utc="0" interval="119">
                        <memory per="second" unit="kB">
                            <memfree>1139716</memfree>
                            <memused>131892</memused>
                            <memused-percent>10.37</memused-percent>
                            <buffers>11664</buffers>
                            <cached>52192</cached>
                            <commit>509148</commit>
                            <commit-percent>28.79</commit-percent>
                            <active>57384</active>
                            <inactive>29948</inactive>
                            <dirty>76</dirty>
                        </memory>
                        <network per="second">
                            <net-dev iface="lo" rxpck="0.00" txpck="0.00" rxkB="0.00" txkB="0.00" rxcmp="0.00" txcmp="0.00" rxmcst="0.00" ifutil-percent="0.00"/>
                            <net-dev iface="eth0" rxpck="13.35" txpck="12.40" rxkB="13.68" txkB="0.91" rxcmp="0.00" txcmp="0.00" rxmcst="0.00" ifutil-percent="0.00"/>
                        </network>
                    </timestamp>
</statistics>
        </host>
    </sysstat>

My goal is given a timestamp interval, such as between date="2017-04-10" time="07:50:12" and date="2017-04-10" time="07:52:01", print out memused and rxpck using Python.

I started the code:

from xml.dom import minidom

doc = minidom.parse("arq.xml")

# doc.getElementsByTagName returns NodeList
timestamp = doc.getElementsByTagName("timestamp")[0]
print(timestamp.firstChild.data)

But I won’t. Someone could help?

Let’s assume that in XML you had a day with several different times. What I wanted was to print these values for all times contained in the XML file.

Example of such an XML: https://ufile.io/4yd3x

Answer 1

First you need to set the date thresholds that your script has to work on. For this you should use the library datetime:

from datetime import datetime

begin = datetime(2017, 4, 10, 7, 50, 12)
end = datetime(2017, 4, 10, 7, 52, 1)

Then you have to iterate over all the tags timestamp, obtain their date and time and filter those that are not in the crease defined. Get the attributes date and time with the method getAttribute() and make the interpretation of strings with the datetime.strptime():

for timestamp in doc.getElementsByTagName('timestamp'):
    date = timestamp.getAttribute('date')
    time = timestamp.getAttribute('time')
    dt = datetime.strptime('%s %s' % (date, time), '%Y-%m-%d %H:%M:%S')
    if dt < begin or dt >= end:
        continue

Okay, now just get the contents of tag memused, iterate over all network interfaces (tags net-dev) and obtain the desired attributes (rxpck and maybe iface):

memused = timestamp.getElementsByTagName('memused')[0].firstChild.data
for netdev in timestamp.getElementsByTagName('net-dev'):
    iface = netdev.getAttribute('iface')
    rxpck = netdev.getAttribute('rxpck')
    print 'date:%s time:%s memused:%s iface:%s rxpck:%s' % (date, time, memused, iface, rxpck)

Below is the complete code for easy testing:

#!/usr/bin/env python

from xml.dom import minidom
from datetime import datetime

doc = minidom.parse('arq.xml')

begin = datetime(2017, 4, 10, 7, 50, 12)
end = datetime(2017, 4, 10, 7, 52, 1)

for timestamp in doc.getElementsByTagName('timestamp'):
    date = timestamp.getAttribute('date')
    time = timestamp.getAttribute('time')
    dt = datetime.strptime('%s %s' % (date, time), '%Y-%m-%d %H:%M:%S')
    if dt < begin or dt >= end:
        continue
    memused = timestamp.getElementsByTagName('memused')[0].firstChild.data
    for netdev in timestamp.getElementsByTagName('net-dev'):
        iface = netdev.getAttribute('iface')
        rxpck = netdev.getAttribute('rxpck')
        print 'date:%s time:%s memused:%s iface:%s rxpck:%s' % (date, time, memused, iface, rxpck)

For more information on handling XML files in Python I recommend reading manual of minidom (in English only, unfortunately) or the answers to that question.