seen with the current 2.7 branch:

$ cat > x.py
def foo(): yield
gen = foo()
print gen.gi_frame.f_restricted
for i in gen: pass
print gen.gi_frame
gen = foo()
print gen.next()
print gen.gi_frame.f_restricted

$ python x.py 
False
None
None
Segmentation fault

Program received signal SIGSEGV, Segmentation fault.
0x0000000000462b44 in frame_getrestricted (
    f=Frame 0x7ffff7f58410, for file x.py, line 1, in foo (), closure=0x0)
    at ../Objects/frameobject.c:383
383     ../Objects/frameobject.c: No such file or directory.
(gdb) bt
#0  0x0000000000462b44 in frame_getrestricted (
    f=Frame 0x7ffff7f58410, for file x.py, line 1, in foo (), closure=0x0)
    at ../Objects/frameobject.c:383

This is related to the fix for issue 14432. gen_send_ex sets f->f_tstate to NULL, so PyFrame_IsRestricted segfaults: 

    #define PyFrame_IsRestricted(f) \
        ((f)->f_builtins != (f)->f_tstate->interp->builtins)

Related change:

New changeset aa324af42c0e by Victor Stinner in branch '2.7':
Issue #14432: Generator now clears the borrowed reference to the thread state
http://hg.python.org/cpython/rev/aa324af42c0e

This appears to be 2.7 only as 3.4.2 stops on the first print with AttributeError: 'frame' object has no attribute 'f_restricted', which is not a crash.

The fix for issue 14432 was applied to 3.3, but I'm pretty sure 2.x PyFrame_IsRestricted is the only problem. Nothing else should see f_tstate when it's NULL. Also, f_tstate was dropped from PyFrameObject in 3.4.

New changeset 68ddb59417ee0b0dedf5c8b66a304138c9ce0a63 by Serhiy Storchaka (Zackery Spytz) in branch '2.7':
[2.7] bpo-22851: Fix a segfault when accessing generator.gi_frame.f_restricted. (GH-9348)
https://github.com/python/cpython/commit/68ddb59417ee0b0dedf5c8b66a304138c9ce0a63