writing xml to file python multiple times

Question

I seem to be stuck. I am trying to get multiple iterations of the xml that is generated from my python code. It only writes the latest iteration to file.

Here is my code:

import xml.etree.cElementTree as ET
from random import randint

i=5
while i>-4:
  event = ET.Element("event")
  event.set("class", "rer")
  event.set("id", "EV_%d" % (i))
  event.set("date", "${ev_d}")

  loc = ET.SubElement(event, "loc")
  flir = ET.SubElement(loc, "flir")

  de = ET.SubElement(flir, "de")
  de.set("dist", "km")
  de.set("val", "%d" % (randint(0,2)))

  i -=1   

  tree = ET.ElementTree(event)
  tree.write("test.xml")

What I get:

<event class="rer" date="${ev_d}" id="EV_-3">
  <loc>
    <flir>
      <de dist="km" val="0" />
    </flir>
  </loc>
</event>

What I want in the output file:

<event class="rer" date="${ev_d}" id="EV_5">
  <loc>
    <flir>
      <de dist="km" val="0" />
    </flir>
  </loc>
</event>
<event class="rer" date="${ev_d}" id="EV_4">
  <loc>
    <flir>
      <de dist="km" val="0" />
    </flir>
  </loc>
</event>
<event class="rer" date="${ev_d}" id="EV_3">
  <loc>
    <flir>
      <de dist="km" val="0" />
    </flir>
  </loc>
</event>

Thanks in advance for your help.

Regards, merit_2

What you want is invalid XML. An XML document must consist of a single element at the top level, not multiple elements. — jwodder, Mar 15 '16 at 16:27
1. `ElementTree.write` does not append to a file. 2. What is the purpose of `i`? In your code it doesn't look like it ever gets updated, so this will just run forever.. — user812786, Mar 15 '16 at 16:27
Sorry, I edited out my decrement statement. I see that I am not appending my file, but I don't understand how to do so. I know this is not well formatted xml, its a component of what I am trying to make. — merit_2, Mar 15 '16 at 16:32
Ok, thanks for the clarification. In that case, have you seen http://stackoverflow.com/questions/13657341/how-do-i-append-new-data-to-existing-xml-using-python-elementtree ? — user812786, Mar 15 '16 at 16:51

score 1 · Answer 1 · answered Mar 15 '16 at 16:57

You continually overwrite event in the while loop - so naturally you have just on event which gets printed. You need to do something like:

import xml.etree.cElementTree as ET
from random import randint

i = 5
events = []
while i > -4:
    event = ET.Element("event")
    event.set("class", "rer")
    event.set("id", "EV_%d" % (i))
    event.set("date", "${ev_d}")
    loc = ET.SubElement(event, "loc")
    flir = ET.SubElement(loc, "flir")
    de = ET.SubElement(flir, "de")
    de.set("dist", "km")
    de.set("val", "%d" % (randint(0, 2)))
    events.append(event)
    i -= 1

with open('output.xml', 'w') as out:
    for event in events:
        tree = ET.ElementTree(event)
        tree.write(out)
        out.write('\n')

score 1 · Accepted Answer · answered Mar 15 '16 at 17:16

As @jwodder pointed out, your proposed output is not valid XML. Your options are to fix that or get around it. Since you mentioned that this is only a component, here's a way to do it if you have a parent element that each <event> will be nested under.

import xml.etree.cElementTree as ET
from random import randint

parent = ET.Element("parent")
tree = ET.ElementTree(parent)

i=5
while i>-4:
    event = ET.Element("event")
    event.set("class", "rer")
    event.set("id", "EV_%d" % (i))
    event.set("date", "${ev_d}")

    loc = ET.SubElement(event, "loc")
    flir = ET.SubElement(loc, "flir")

    de = ET.SubElement(flir, "de")
    de.set("dist", "km")
    de.set("val", "%d" % (randint(0,2)))

    i -=1   

    parent.append(event)

tree.write("test.xml")

Here I added the parent element and append-ed event to the parent, then wrote the parent tree out to file at the end.

Output:

<parent>
  <event class="rer" date="${ev_d}" id="EV_5">
    <loc>
      <flir>
        <de dist="km" val="1" />
      </flir>
    </loc>
  </event>
  <event class="rer" date="${ev_d}" id="EV_4">
    <loc>
      <flir>
        <de dist="km" val="2" />
      </flir>
    </loc>
  </event>
  <event class="rer" date="${ev_d}" id="EV_3">
    <loc>
      <flir>
        <de dist="km" val="2" />
      </flir>
    </loc>
  </event>
  <event class="rer" date="${ev_d}" id="EV_2">
    <loc>
      <flir>
        <de dist="km" val="1" />
      </flir>
    </loc>
  </event>
  <event class="rer" date="${ev_d}" id="EV_1">
    <loc>
      <flir>
        <de dist="km" val="2" />
      </flir>
    </loc>
  </event>
  <event class="rer" date="${ev_d}" id="EV_0">
    <loc>
      <flir>
        <de dist="km" val="0" />
      </flir>
    </loc>
  </event>
  <event class="rer" date="${ev_d}" id="EV_-1">
    <loc>
      <flir>
        <de dist="km" val="2" />
      </flir>
    </loc>
  </event>
  <event class="rer" date="${ev_d}" id="EV_-2">
    <loc>
      <flir>
        <de dist="km" val="0" />
      </flir>
    </loc>
  </event>
  <event class="rer" date="${ev_d}" id="EV_-3">
    <loc>
      <flir>
        <de dist="km" val="2" />
      </flir>
    </loc>
  </event>
</parent>

Glad to hear it! Don't forget to upvote or accept helpful answers :) — user812786, Mar 15 '16 at 19:31

writing xml to file python multiple times

2 Answers2