A Possible bug in Cython? This is the code for a message that I'm posting to the cython-users group at https://groups.google.com/forum/#!forum/cython-users

hello.pyx

cdef struct MyStruct:
    int x

def byte_bugginess(x=1):
    cdef char val = 1
    cdef MyStruct foo

    print("1 - val = %d" % val)

    if x in (3, 4):
        print("2 - val = %d" % val)
        val = 2
        print("3 - val = %d" % val)
    else:
        print("4 - val = %d" % val)
        val = foo.x
        print("5 - val = %d" % val)

    print("6 - val = %d" % val)

Makefile

test: hello.so
	python -c 'import hello; hello.byte_bugginess()'

hello.so: hello.pyx
	python setup.py build_ext --inplace

clean:
	$(RM) -r *.so *.c *.pyc __pycache__ *.egg-info build

setup.py

import sys

try:
    from setuptools import setup
    from setuptools.extension import Extension
except ImportError:
    print("Couldn't import setuptools. Falling back to distutils.")
    from distutils.core import setup

#
# Force `setup_requires` stuff like Cython to be installed before proceeding
#
from setuptools.dist import Distribution
Distribution(dict(setup_requires='Cython'))

try:
    from Cython.Distutils import build_ext
except ImportError:
    print("Could not import Cython.Distutils. Install `cython` and rerun.")
    sys.exit(1)

ext_modules = [Extension("hello", ["hello.pyx"])]

setup(
  name = 'Hello world app',
  cmdclass = {'build_ext': build_ext},
  ext_modules = ext_modules,
  setup_requires = ['Cython'],
  test_suite='test',
)

Sample output

marca@marca-mac:~/dev/git-repos/cython-test$ make
python setup.py build_ext --inplace
running build_ext
gcc-4.2 not found, using clang instead
cythoning hello.pyx to hello.c
building 'hello' extension
creating build
creating build/temp.macosx-10.6-intel-2.7
clang -fno-strict-aliasing -fno-common -dynamic -isysroot /Developer/SDKs/MacOSX10.6.sdk -arch i386 -arch x86_64 -g -O2 -DNDEBUG -g -O3 -I/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c hello.c -o build/temp.macosx-10.6-intel-2.7/hello.o
clang -bundle -undefined dynamic_lookup -arch i386 -arch x86_64 -isysroot /Developer/SDKs/MacOSX10.6.sdk -isysroot /Developer/SDKs/MacOSX10.6.sdk -g build/temp.macosx-10.6-intel-2.7/hello.o -o /Users/marca/dev/git-repos/cython-test/hello.so
python -c 'import hello; hello.byte_bugginess(1)'
1 - val = 1
4 - val = 1
5 - val = 0
6 - val = 2

How the heck is val == 2?