Update some python examples to python 3 syntax.

Update some sample code snippets in comments to use python 3 syntax.

assigned to @clemenci

changed milestone to %v34r1

approved this merge request

I do not know why the pipeline failed, but I do not believe it is caused by these changes, so I'll force the merge.

mentioned in commit clemenci/Gaudi@ea09f64d

mentioned in commit clemenci/Gaudi@41755f37

merged