llvm-project/lldb/packages/Python/lldbsuite/support/optional_with.py

# ====================================================================
# Provides a with-style resource handler for optionally-None resources
# ====================================================================


class optional_with(object):
    # pylint: disable=too-few-public-methods
    # This is a wrapper - it is not meant to provide any extra methods.
    """Provides a wrapper for objects supporting "with", allowing None.

    This lets a user use the "with object" syntax for resource usage
    (e.g. locks) even when the wrapped with object is None.

    e.g.

    wrapped_lock = optional_with(thread.Lock())
    with wrapped_lock:
        # Do something while the lock is obtained.
        pass

    might_be_none = None
    wrapped_none = optional_with(might_be_none)
    with wrapped_none:
        # This code here still works.
        pass

    This prevents having to write code like this when
    a lock is optional:

    if lock:
        lock.acquire()

    try:
        code_fragment_always_run()
    finally:
        if lock:
            lock.release()

    And I'd posit it is safer, as it becomes impossible to
    forget the try/finally using optional_with(), since
    the with syntax can be used.
    """

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

    def __enter__(self):
        if self.wrapped_object is not None:
            return self.wrapped_object.__enter__()
        else:
            return self

    def __exit__(self, the_type, value, traceback):
        if self.wrapped_object is not None:
            return self.wrapped_object.__exit__(the_type, value, traceback)
        else:
            # Don't suppress any exceptions
            return False