Self-referencing tuple in 32-bit CPython 2.7.

selfreferencingtuple.py

import ctypes
import struct
import sys

# Goal: obtain something like "outer = (outer,)", even though that's impossible with vanilla Python
inner = ()
outer = (inner,)

# Get CPython's internal representation of the outer tuple
c_outer = (ctypes.c_char * sys.getsizeof(outer)).from_address(id(outer))

# Find where it keeps the pointer to the inner tuple
inner_index = c_outer[:].find(struct.pack('P', id(inner)))

# Replace the inner tuple's address with that of the outer tuple
c_outer[inner_index:inner_index+struct.calcsize('P')] = struct.pack('P', id(outer))

# Tuples don't handle self-references very well...
print outer