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Python object replacement demonstration, from https://benkurtovic.com/2015/01/28/python-object-replacement.html
import ctypes
from ctypes import pythonapi as api
import sys
from types import (BuiltinFunctionType, GetSetDescriptorType, FrameType,
MemberDescriptorType, MethodType)
import guppy
from guppy.heapy import Path
hp = guppy.hpy()
def _w(x):
def f():
x
return f
CellType = type(_w(0).func_closure[0])
del _w
# -----------------------------------------------------------------------------
def _write_struct_attr(addr, value, add_offset):
ptr_size = ctypes.sizeof(ctypes.py_object)
ptrs_in_struct = (3 if hasattr(sys, "getobjects") else 1) + add_offset
offset = ptrs_in_struct * ptr_size + ctypes.sizeof(ctypes.c_ssize_t)
ref = ctypes.byref(ctypes.py_object(value))
ctypes.memmove(addr + offset, ref, ptr_size)
def _replace_attribute(source, rel, new):
if isinstance(source, (MethodType, BuiltinFunctionType)):
if rel == "__self__":
# Note: PyMethodObject->im_self and PyCFunctionObject->m_self
# have the same offset
_write_struct_attr(id(source), new, 1)
return
if rel == "im_self":
return # Updated via __self__
if isinstance(source, type):
if rel == "__base__":
return # Updated via __bases__
if rel == "__mro__":
return # Updated via __bases__ when important, otherwise futile
if isinstance(source, (GetSetDescriptorType, MemberDescriptorType)):
if rel == "__objclass__":
_write_struct_attr(id(source), new, 0)
return
try:
setattr(source, rel, new)
except TypeError as exc:
print "Unknown R_ATTRIBUTE (read-only):", rel, type(source)
def _replace_indexval(source, rel, new):
if isinstance(source, tuple):
temp = list(source)
temp[rel] = new
replace(source, tuple(temp))
return
source[rel] = new
def _replace_indexkey(source, rel, new):
source[new] = source.pop(source.keys()[rel])
def _replace_interattr(source, rel, new):
if isinstance(source, CellType):
api.PyCell_Set(ctypes.py_object(source), ctypes.py_object(new))
return
if rel == "ob_type":
source.__class__ = new
return
print "Unknown R_INTERATTR:", rel, type(source)
def _replace_local_var(source, rel, new):
source.f_locals[rel] = new
api.PyFrame_LocalsToFast(ctypes.py_object(source), ctypes.c_int(0))
_RELATIONS = {
Path.R_ATTRIBUTE: _replace_attribute,
Path.R_INDEXVAL: _replace_indexval,
Path.R_INDEXKEY: _replace_indexkey,
Path.R_INTERATTR: _replace_interattr,
Path.R_LOCAL_VAR: _replace_local_var
}
def _path_key_func(path):
reltype = type(path.path[1]).__bases__[0]
return 1 if reltype is Path.R_ATTRIBUTE else 0
def replace(old, new):
for path in sorted(hp.iso(old).pathsin, key=_path_key_func):
relation = path.path[1]
try:
func = _RELATIONS[type(relation).__bases__[0]]
except KeyError:
print "Unknown relation:", relation, type(path.src.theone)
continue
func(path.src.theone, relation.r, new)
# -----------------------------------------------------------------------------
class A(object):
def func(self):
return self
class B(object):
pass
class X(object):
pass
def sure(obj):
def inner():
return obj
return inner
def gen(obj):
while True:
yield obj
class S(object):
__slots__ = ("p", "q")
class T(object):
__slots__ = ("p", "q")
class U(object):
pass
class V(object):
pass
class W(U):
pass
# -----------------------------------------------------------------------------
a = A()
b = B()
X.cattr = a
x = X()
x.iattr = a
d = {a: a}
L = [a]
t = (a,)
f = a.func
meth = a.__sizeof__
clo = sure(a)
g = gen(a)
s = S()
s.p = a
u = U()
ud = U.__dict__["__dict__"]
s.q = S
sd = S.q
# -----------------------------------------------------------------------------
def examine_vars(id1, id2, id3):
ex = lambda v, id_: str(v) + ("" if id(v) == id_ else " - ERROR!")
print "dict (local var): ", ex(a, id1)
print "dict (class attr): ", ex(X.cattr, id1)
print "dict (inst attr): ", ex(x.iattr, id1)
print "dict (key): ", ex(d.keys()[0], id1)
print "dict (value): ", ex(d.values()[0], id1)
print "list: ", ex(L[0], id1)
print "tuple: ", ex(t[0], id1)
print "method (instance): ", ex(f(), id1)
print "method (builtin): ", ex(meth.__self__, id1)
print "closure: ", ex(clo(), id1)
print "frame (generator): ", ex(next(g), id1)
print "slots: ", ex(s.p, id1)
print "class (instance): ", ex(type(u), id2)
print "class (subclass): ", ex(W.__bases__[0], id2)
print "class (g/s descr): ", ex(ud.__get__(u, U) or type(u), id2)
print "class (mem descr): ", ex(sd.__get__(s, S), id3)
if __name__ == "__main__":
examine_vars(id(a), id(U), id(S))
print "-" * 35
replace(a, b)
replace(U, V)
replace(S, T)
print "-" * 35
examine_vars(id(b), id(V), id(T))
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