Context Manager without Yield

Can I have a context manager which occasionally does not yield, and in which case the code within the with statement are simply not executed?

import contextlib

@contextlib.contextmanager
def MayNotYield(to_yield):
  if to_yield:
    yield

with MayNotYield(True):  
  print 'This works.'

with MayNotYield(False):  
  print 'This errors.'

I could ask the user to wrap the with statement with a try-catch, but that is not preferred. I could also do the following but it is ugly too.

import contextlib

@contextlib.contextmanager
def AlwaysYields(to_yield):
  if to_yield:
    yield 1
  else:
    yield 2

with AlwaysYields(True) as result:
  if result == 1:
    print 'This works.'

Unfortunately, the context manager protocol does not give a context manager a way to say "Don't run the with block" (except raising an exception in __enter__). If you're using a context manager anyway, I think your second approach, which has __enter__ return a value to signal if the block should be run is the best approach. If you don't need a context manager for some other reason, you could just use a simple if statement:

if do_stuff:
    # do the stuff