import sys

class GeneratorContextManager(object):

           def __init__(self, gen):
               self.gen = gen

           def __enter__(self):
               try:
                   return self.gen.next()
               except StopIteration:
                   raise RuntimeError("generator didn't yield")

           def __exit__(self, type, value, traceback):
               if type is None:
                   try:
                       self.gen.next()
                   except StopIteration:
                       return
                   else:
                       raise RuntimeError("generator didn't stop")
               else:
                   try:
                       self.gen.throw(type, value, traceback)
                       raise RuntimeError("generator didn't stop after throw()")
                   except StopIteration:
                       return True
                   except:
                       # only re-raise if it's *not* the exception that was
                       # passed to throw(), because __exit__() must not raise
                       # an exception unless __exit__() itself failed.  But
                       # throw() has to raise the exception to signal
                       # propagation, so this fixes the impedance mismatch
                       # between the throw() protocol and the __exit__()
                       # protocol.
                       #
#                       if sys.exc_info()[1] is not value:
                       raise

def contextmanager(func):
    def helper(*args, **kwds):
        return GeneratorContextManager(func(*args, **kwds))
    return helper