You can't. with doesn't support "skip the body" — calling __exit__ inside __enter__ just runs cleanup code early; the block still executes. __exit__ isn't a "leave the with block" operation, it's just a method call.

The only way __enter__ can prevent the body from running is by raising an exception, which propagates and skips the block (and runs outer handlers, if any):

class ChangeUI:
    def __enter__(self):
        raise RuntimeError('UI change not available')
    def __exit__(self, *_):
        return

try:
    with ChangeUI() as changeUI:
        print(f'{changeUI=}')  # never runs
except RuntimeError:
    pass

If you want an optional/skippable block, alternatives:

1. Conditionals — the idiomatic choice:

   python

   Copy

   if can_change_ui():
       changeUI = make_change_ui()
       print(f'{changeUI=}')

2. A no-op context + guard inside the block:

   python

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   with ChangeUI() as changeUI:
       if changeUI is not None:
           print(f'{changeUI=}')

   where __enter__ may return None to signal "nothing to do".

3. Generator-based, for early-exit style logic (the body still runs, but you can exit as soon as a condition fails):

   python

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   from contextlib import contextmanager
   
   @contextmanager
   def change_ui():
       ...
       yield

Bottom line: __enter__ can't cancel the with body silently; it can only signal failure via an exception, which you must catch to avoid it propagating.