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Boolean constants get confused with integers #2919

st-pasha opened this Issue Apr 11, 2019 · 1 comment


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commented Apr 11, 2019

We found that our regular Python code compiled with Cython behaves differently from the original. The issue appears to be with boolean constants being treated as if they were integers 0/1 (or the other way around). The following MRE reproduces the problem:


# cython: language_level=3

def test():
    j = (False, False)
    k = (0, 0)
    if k[0] is False or k[1] is False:
        raise AssertionError("Oh noes! k = %r" % (k,))

from distutils.core import setup
from Cython.Build import cythonize
setup(ext_modules = cythonize('dt.pyx'))


$ python build_ext --inplace
Compiling dt.pyx because it changed.
[1/1] Cythonizing dt.pyx
running build_ext
building 'dt' extension
gcc -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -arch x86_64 -g -I/Library/Frameworks/Python.framework/Versions/3.6/include/python3.6m -c dt.c -o build/temp.macosx-10.9-x86_64-3.6/dt.o
gcc -bundle -undefined dynamic_lookup -arch x86_64 -g build/temp.macosx-10.9-x86_64-3.6/dt.o -o /Users/pasha/github/datatable/temp/cy/


$ python
Python 3.6.6 (v3.6.6:4cf1f54eb7, Jun 26 2018, 19:50:54) 
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from dt import test
>>> test()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "dt.pyx", line 7, in dt.test
    raise AssertionError("Oh noes! k = %r" % (k,))
AssertionError: Oh noes! k = (False, False)
>>> def test():
...     j = (False, False)
...     k = (0, 0)
...     if k[0] is False or k[1] is False:
...         raise AssertionError("Oh noes! k = %r" % (k,))
...     print("ok")
>>> test()

Using Cython version 0.29.6 (


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commented Apr 12, 2019

Thanks for the report. My guess is that both tuples are treated as typed ctuples, but that the type deduplication for them does not distinguish the int and bint types and joins both together into (bint, bint). It probably also depends on the order in which you define the tuples.

The deduplication happens in declare_tuple_type() in It's worth investigating how the hashing and comparison works for the types at hand, to see what can be improved there.

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