Frank Millman, 26.08.2013 08:24:

I noticed a behaviour in lxml that surprised me, so I thought I would mention it.

Versions - python 3.3.2, lxml 3.2.1.

Consider the following - standard python slicing -

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a = [1, 2, 3, 4] b = [5, 6, 7, 8] a[:0] = b[0:] a [5, 6, 7, 8, 1, 2, 3, 4] b [5, 6, 7, 8]

This is what I expected.

Then look at this - lxml slicing -

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from lxml import etree a = etree.fromstring('<a1><a1.1/><a1.2/></a1>') b = etree.fromstring('<b1><b1.1/><b1.2/></b1>') a[:0] = b[0:] etree.tostring(a) b'<a1><b1.1/><b1.2/><a1.1/><a1.2/></a1>' etree.tostring(b) b'<b1/>'

The slicing worked, but it removed the contents of b.

Is this intentional?

Yes, it's intentional and documented in a couple of places, e.g. here http://lxml.de/tutorial.html#elements-are-lists Stefan