pythonconditional-statementsindentationwith-statement

Conditional with statement in Python


Is there a way to begin a block of code with a with statement, but conditionally?

Something like:

if needs_with():
    with get_stuff() as gs:

# do nearly the same large block of stuff,
# involving gs or not, depending on needs_with()

To clarify, one scenario would have a block encased in the with statement, while another possibility would be the same block, but not encased (i.e., as if it wasn't indented)

Initial experiments of course give indentation errors..


Solution

  • If you want to avoid duplicating code and are using a version of Python prior to 3.7 (when contextlib.nullcontext was introduced) or even 3.3 (when contextlib.ExitStack was introduced), you could do something like:

    class dummy_context_mgr():
        def __enter__(self):
            return None
        def __exit__(self, exc_type, exc_value, traceback):
            return False
    

    or:

    import contextlib
    
    @contextlib.contextmanager
    def dummy_context_mgr():
        yield None
    

    and then use it as:

    with get_stuff() if needs_with() else dummy_context_mgr() as gs:
       # do stuff involving gs or not
    

    You alternatively could make get_stuff() return different things based on needs_with().

    (See Mike's answer or Daniel's answer for what you can do in later versions.)