Python Monkey Patching Function Globals

class GlobalCaller(object):

  def __init__(self, method, value):
    self.method = method
    self.value = value

  def __call__(self, *args, **kwargs):
    added = False
    curr_globals = self.method.func_globals
    if 'a' not in curr_globals:
      curr_globals['a'] = self.value
      added = True
    result = self.method(*args, **kwargs)
    if added:
      curr_globals.pop('a')
    return result


def deco(value):

  def actual_deco(method):

    return GlobalCaller(method, value)

  return actual_deco


@deco(99)
def f():
  return a


@deco(9)
def g(b):
  return a + b


print f()
print g(1)