Tail Call Optimization Decorator (Python recipe)

This decorator implements tail call optimization through stack introspection.

#!/usr/bin/env python2.4# This program shows off a python decorator(# which implements tail call optimization. It# does this by throwing an exception if it is # it's own grandparent, and catching such # exceptions to recall the stack.import sysclass TailRecurseException:  def __init__(self, args, kwargs):    self.args = args    self.kwargs = kwargsdef tail_call_optimized(g):  """  This function decorates a function with tail call  optimization. It does this by throwing an exception  if it is it's own grandparent, and catching such  exceptions to fake the tail call optimization.    This function fails if the decorated  function recurses in a non-tail context.  """  def func(*args, **kwargs):    f = sys._getframe()    if f.f_back and f.f_back.f_back \        and f.f_back.f_back.f_code == f.f_code:      raise TailRecurseException(args, kwargs)    else:      while 1:        try:          return g(*args, **kwargs)        except TailRecurseException, e:          args = e.args          kwargs = e.kwargs  func.__doc__ = g.__doc__  return func@tail_call_optimizeddef factorial(n, acc=1):  "calculate a factorial"  if n == 0:    return acc  return factorial(n-1, n*acc)print factorial(10000)# prints a big, big number,# but doesn't hit the recursion limit.@tail_call_optimizeddef fib(i, current = 0, next = 1):  if i == 0:    return current  else:    return fib(i - 1, next, current + next)print fib(10000)# also prints a big number,# but doesn't hit the recursion limit.