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This simple script segfaults the interpreter (all versions), at least when run with "./python myscript.py"
myscript.py::
 import sys
 del sys.module['__main__']

Many paths in pythonrun.c contains these lines:
 m = PyImport_AddModule("__main__");
 d = PyModule_GetDict(m);
both return borrowed references, from sys.modules.
in most cases, d is simply passed to PyEval_EvalCode() and not used afterwards, *except* in PyRun_SimpleFileExFlags which calls PyDict_DelItemString(d, "__file__"); this is where the crash occurs.

Attached patch changes PyRun_SimpleFileExFlags() to keep a reference to the module.

Fun fact, on 2.7 & 3.2 I get infinite loops @ 100% CPU. 3.3 & default crash.
Unless someone yells, I'll polish this up and commit next week.

I was unable to reproduce the case with stock python 2.7 neither on OSX nor on Linux. System python 3.2 seems to be fine too. 
At the same time python 2.7 built with debug enabled gets infinite loop and uses all the cpu.
However, python 3.4 crashes just as described built both with or without debug flag, and suggested patch fixes it.

Same here, I tested the patch on 3.4 (debug and non-debug) and it seems to fix the problem.

New changeset b256d054f229 by Hynek Schlawack in branch '3.2':
Issue #15001: fix segfault on "del sys.module['__main__']"
http://hg.python.org/cpython/rev/b256d054f229
New changeset 215297665098 by Hynek Schlawack in branch '3.3':
Issue #15001: fix segfault on "del sys.module['__main__']"
http://hg.python.org/cpython/rev/215297665098
New changeset 859ef54bdce2 by Hynek Schlawack in branch 'default':
Issue #15001: fix segfault on "del sys.module['__main__']"
http://hg.python.org/cpython/rev/859ef54bdce2 

New changeset 4ebe1ede981e by Hynek Schlawack in branch '2.7':
Issue #15001: fix segfault on "del sys.modules['__main__']"
http://hg.python.org/cpython/rev/4ebe1ede981e 

This should be fixed now, thanks to all who helped!