Control attribute ordering with ElementTree

Question

I am trying to compare two xml files, which have different formatting but similar content. The way I am going about this is:

1. Parse XML files with ElementTree
2. Pretty print the xml content, so that we get a normalized format. For this I am using either ElementTree.tostring or ElementTree.write
3. Now use any tool to compare the normalized files (textual comparisson)

This works fine, but a big problem remains: I am unable to control the order of the attributes in the nodes.

Is it possible to force a certain attribute sort order with ElementTree?

I do not want to keep the original attribute order, but provide a sort mechanism myself, so that, no matter how the original files look like, the normalized files will have the same attribute order.