Hi Cython devs, Over in scikit-image we have traced an odd problem with a particular Cython file to the 0.19 update of Cython. From at least Cython 0.15.1 (probably earlier) through 0.18, `_mcp.pyx` in `skimage.graph` compiled and executed correctly, passing all package tests on both Python 2.7 and Python 3.
After 0.19 was released and the Travis builds began using it, we began getting 100% repeatable errors from the previously clean master branch (example of an otherwise clean Python 2.7<https://travis-ci.org/scikit-image/scikit-image/jobs/6545505>Travis build; the Python 3 build passed<https://travis-ci.org/scikit-image/scikit-image/builds/6545504>all tests). All of these errors/failures trace back to this Cython file. Oddly, the errors only happen on Python 2.7; our Python 3 Travis build passes. We are discussing this issue in scikit-image Github Issue #534<https://github.com/scikit-image/scikit-image/issues/534>; feel free to join the discussion there. The .pyx Cython file is located here<https://github.com/scikit-image/scikit-image/blob/master/skimage/graph/_mcp.pyx>and it has an associated .pxd file here<https://github.com/scikit-image/scikit-image/blob/master/skimage/graph/_mcp.pxd>. It should be noted the file compiles and executes without errors, but its output is now incorrect in Python 2.x. In case the compiled results might be relevant, for your diffing pleasure here is the compiled .c file from Cython 0.18<https://gist.github.com/JDWarner/af4f8ea85dce356ce95c>which passes all tests on both Python 2.7 and Python 3.x, while here is the compiled .c file from Cython 0.19<https://gist.github.com/JDWarner/56d15b7a7527b8d4314e>which produces different, incorrect results in Python 2.7. In the short term we are temporarily forcing Travis to use the 0.18 release of Cython, but that isn't a viable long term solution. It's possible the error is on our end, but seeing as it worked with prior Cython releases we'd appreciate you taking a look. Thanks!
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