A simple example on how to patch a constant in a python 2 function

patch_const.py

import new


class Empty(object):
  pass


def patch_const(func, const_index, new_value, previous_value=Empty):
  co = func.func_code
  consts = list(co.co_consts)
  if previous_value is not Empty:
    if consts[const_index] != previous_value:
      raise RuntimeError('Wrong value for const: %s' % (consts[const_index]))
  consts[const_index] = new_value
  consts = tuple(consts)
  new_code = new.code(co.co_argcount, co.co_nlocals, co.co_stacksize, co.co_flags, co.co_code, consts, co.co_names, co.co_varnames, co.co_filename, co.co_name, co.co_firstlineno, co.co_lnotab)
  func.func_code = new_code