[C++-sig] Rational for 'Zero-length slice' RuntimeError? (original) (raw)

Hans Meine meine at informatik.uni-hamburg.de
Mon Jan 5 15:43:06 CET 2009

On Sonntag 04 Januar 2009, Hans Meine wrote:

I have exported an array-like class using the getitem implementation given below among its overloads. It uses boost::python::slice.getindices(), and I am getting a RuntimeError when I try to acces e.g. [1:-1] on a 2-element array. What is the rationale for this "Zero-length slice" error? I would expect an empty iterator range. OK, if end < begin, that could make problems, but what am I expected to do to prevent this RuntimeError? (Yes, I did RTFM, but maybe I am overlooking something?)

Yes, I was overlooking quite some things. Quoting the docs:

Rationale: [...] exceptions on empty slice: It is impossible to define a closed interval over an empty range, so some other form of error checking would have to be used to prevent undefined behavior. In the case where the exception is not caught, it will simply be translated to Python by the default exception handling mechanisms.

I was tired and the automatic translation of std::invalid_argument into a RuntimeError obviously outsmarted me.

So obviously, the answer is that I have to copy the boilerplate-try..catch from the docs (and handle the empty interval case).

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