PyKML : appending a Placemark to more than one KML document

Question

I am using PyKML to create several KML files and am running into some strange behavior that I hope someone can explain. The following reproduces the problem:

from lxml import etree
from pykml.factory import KML_ElementMaker as KML

doc1 = KML.kml(KML.Document())
doc2 = KML.kml(KML.Document())

p = KML.Placemark()

doc1.Document.append(p)
doc2.Document.append(p)

print etree.tostring(etree.ElementTree(doc1),pretty_print=True)
print etree.tostring(etree.ElementTree(doc2),pretty_print=True)

and here is the output :

<kml xmlns:gx="http://www.google.com/kml/ext/2.2"    xmlns:atom="http://www.w3.org/2005/Atom" xmlns="http://www.opengis.net/kml/2.2">
  <Document/>
</kml>

<kml xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:atom="http://www.w3.org/2005/Atom" xmlns="http://www.opengis.net/kml/2.2">
  <Document>
    <Placemark/>
  </Document>
</kml>

The place mark shows up in the second document, but not in the first. It is as if the Placemark can only be appended to one file at a time.

If I rearrange the last few lines as follows, things work.

doc1.Document.append(p)
print etree.tostring(etree.ElementTree(doc1),pretty_print=True)

doc2.Document.append(p)
print etree.tostring(etree.ElementTree(doc2),pretty_print=True)

and the output :

<kml xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:atom="http://www.w3.org/2005/Atom" xmlns="http://www.opengis.net/kml/2.2">
  <Document>
    <Placemark/>
  </Document>
</kml>

<kml xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:atom="http://www.w3.org/2005/Atom" xmlns="http://www.opengis.net/kml/2.2">
  <Document>
    <Placemark/>
  </Document>
</kml>

But this would require major restructuring of my code, which I am hoping to avoid.

I suspect I am missing something fundamental about how PyKML, lxml, elementtree or even Python works. Can someone please explain what might be happening here?

score 1 · Accepted Answer · answered Apr 21 '15 at 18:36

(partial answer - still hoping for an explanation!)

If I do :

from copy import deepcopy
doc1.Document.append(deepcopy(p))
doc2.Document.append(deepcopy(p))

things work. But still, what is etree.tostring doing to the input objects doc1 and doc2? It is as if they are being altered somehow.

PyKML : appending a Placemark to more than one KML document

1 Answers1