[Python-Dev] Raising assertions on wrong element types in ElementTree (original) (raw)

Stefan Behnel stefan_ml at behnel.de
Fri Mar 16 08:51:07 CET 2012

Eli Bendersky, 16.03.2012 08:38:

The Element class in ElementTree (http://docs.python.org/py3k/library/xml.etree.elementtree.html) has some methods for adding new children: append, insert and extend. Currently the documentation states that extend raises AssertionError when something that's not an Element is being passed to it, and the others don't mention mention this case.

AssertionError is clearly the wrong thing to raise for user input.

There are a number of problems with this:

1. The behavior of append, insert and extend should be similar in this respect 2. AssertionError is not the customary error in such case - TypeError is much more suitable 3. The C implementation of ElementTree actually raises TypeError in all these methods, by virtue of using PyArgParseTuple 4. The Python implementation (at least in 3.2) actually doesn't raise even AssertionError in extend - this was commented out The suggestion for 3.3 (where compatibility between the C and Python implementations gets even more important, since the C one is now being imported by default when available) is to raise TypeError in all 3 methods in the Python implementation, to match the C implementation, and to modify the documentation accordingly.

+1

Stefan

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