According to PEP-343, a with statement translates from: with EXPR as VAR: BLOCK to: mgr = (EXPR) exit = type(mgr).__exit__ # Not calling it yet value = type(mgr).__enter__(mgr) exc = True try: try: VAR = value # Only if “as VAR” is present BLOCK except: # The exceptional case is handled here exc = False … Read more
In Python 2.x and 3.0, 3.1 and 3.2, multiprocessing.Pool() objects are not context managers. You cannot use them in a with statement. Only in Python 3.3 and up can you use them as such. From the Python 3 multiprocessing.Pool() documentation: New in version 3.3: Pool objects now support the context management protocol – see Context … Read more
A with statement does not create a scope (like if, for and while do not create a scope either). As a result, Python will analyze the code and see that you made an assignment in the with statement, and thus that will make the variable local (to the real scope). In Python variables do not … Read more
There are some things you need to consider before trying to answer this question. For example, take the Object constructor. It is a “Standard built-in object”. window.status is part of the Window interface. Obviously, you don’t want status to refer to window.status, but do you want Object to refer to window.Object? The solution to your … Read more
If you have long variablenames and would end up with: UserHandler.GetUser.First.User.FirstName=”Stefan” UserHandler.GetUser.First.User.LastName=”Karlsson” UserHandler.GetUser.First.User.Age=”39″ UserHandler.GetUser.First.User.Sex=”Male” UserHandler.GetUser.First.User.Occupation=”Programmer” UserHandler.GetUser.First.User.UserID=”0″ ….and so on then I would use WITH to make it more readable: With UserHandler.GetUser.First.User .FirstName=”Stefan” .LastName=”Karlsson” .Age=”39″ .Sex=”Male” .Occupation=”Programmer” .UserID=”0″ end with In the later example there are even performance benefit over the first example because in the … Read more
It’s not equivalent, but would this syntax work for you? Animal a = new Animal() { SpeciesName = “Lion”, IsHairy = true, NumberOfLegs = 4 };
One annoyance with using with is that the debugger can’t handle it. So it makes debugging more difficult. A bigger problem is that it is less easy to read the code. Especially if the with statement is a bit longer. procedure TMyForm.ButtonClick(…) begin with OtherForm do begin Left := 10; Top := 20; CallThisFunction; end; … Read more
with doesn’t really replace try/except, but, rather, try/finally. Still, you can make a context manager do something different in exception cases from non-exception ones: class Mgr(object): def __enter__(self): pass def __exit__(self, ext, exv, trb): if ext is not None: print “no not possible” print “OK I caught you” return True with Mgr(): name=”rubicon”/2 #to raise … Read more
Python 3.3 introduced contextlib.ExitStack for just this kind of situation. It gives you a “stack”, to which you add context managers as necessary. In your case, you would do this: from contextlib import ExitStack with ExitStack() as stack: if needs_with(): gs = stack.enter_context(get_stuff()) # do nearly the same large block of stuff, # involving gs … Read more
Your original was not working because the parent of Cells(4, 1) and Cells(4, 1).End(xlDown) was not specified. Prefix any cell address with a period (aka . or full stop) when you are inside a With … End With block. Example: With Worksheets(“Verbs”) wordcount = .Range(.Cells(4, 1), .Cells(4, 1).End(xlDown)).Rows.Count End With Note the .Cells(4, 1) and … Read more