"""
valuestack.py: Demo reading values from Python value stack
Offsets are derived for CPython-2.7.2, 64-bit, production build
air:~ dima$ python valuestack.py
return 0.0911498238164
caught 0.0911498238164
"""
import ctypes, inspect, random
def id2obj(i):
"""convert CPython `id` back to object ref, by temporary pointer swap"""
tmp = None,
try:
ctypes.cast(id(tmp), ctypes.POINTER(ctypes.c_ulong))[3] = i
return tmp[0]
finally:
ctypes.cast(id(tmp), ctypes.POINTER(ctypes.c_ulong))[3] = id(None)
def introspect():
"""pointer on top of value stack is id of the object about to be returned
FIXME adjust for sum(vars, locals) in the introspected function
"""
fr = inspect.stack()[1][0]
print "caught", id2obj(ctypes.cast(id(fr), ctypes.POINTER(ctypes.c_ulong))[47])
def value():
tmp = random.random()
print "return", tmp
return tmp
def foo():
try:
return value()
finally:
introspect()
if __name__ == "__main__":
foo()
