cython crush in runtime using yield

[idokoren1]

Mac OS version 10.14
Python 3.7.3
using cython V0.29.1

The following code compile correctly. but crush in run time:

cython code:

    class GlobalFunctions:
        ITER_FUNC = None

    cdef class INSTANCE:
    
        def do_iter(self, *args, **kwargs):
            yield from GlobalFunctions.ITER_FUNC(*args, **kwargs)

python code:

def user_iter(x=1,b=None):
    for i in range(10):
        yield i

GlobalFunctions.ITER_FUNC = user_iter

t = INSTANCE()
for x in t.do_iter():
    print(x)

[da-woods]

This is to do with generator functions that can receive keyword arguments but aren't passed them. Here's a much simpler example:

def f(**kwargs):
    yield 0
    
f()

It generates a segmentation fault when you import the module.

It crashes in the function __pyx_pf_13iterkwd_crash_f (iterkwd_crash is the module name):

__Pyx_INCREF(__pyx_cur_scope->__pyx_v_kwargs);

__kyx_v_kwargs is NULL. The function is called from __pyx_pw_13iterkwd_crash_1f where __pyx_v_kwargs is recognised as unused and set to 0.

[da-woods]

I can get a few different variants of generated code depending on what I do with kwargs:

def g():
    return 0

def f(**kwargs):
    yield g(**kwargs)
    
f()

gives

if (__pyx_kwds) {
    __pyx_v_kwargs = PyDict_Copy(__pyx_kwds); if (unlikely(!__pyx_v_kwargs)) return NULL;
    __Pyx_GOTREF(__pyx_v_kwargs);
  } else {
    __pyx_v_kwargs = NULL;
  }

(i.e. kwargs is deliberately set to NULL if not passed, thus segfault).

In contrast

def f(**kwargs):
    yield from kwargs.keys()
    
f()

Doesn't crash, since kwargs is initialized to an empty dictionary if not passed

__pyx_v_kwargs = (__pyx_kwds) ? PyDict_Copy(__pyx_kwds) : PyDict_New(); if (unlikely(!__pyx_v_kwargs)) return NULL;