On Monday, 5 March 2018 16:47:02 UTC, Steven D'Aprano wrote:
> On Sun, 04 Mar 2018 16:58:38 -0800, Ooomzay wrote:
>
> > Here is an example of a composite resource using RAII:-
> >
> > class RAIIFileAccess():
> > def __init__(self, fname):
> > print("%s Opened" % fname)
> > def __del__(self):
> > print("%s Closed" % fname)
> >
> > class A():
> > def __init__(self):
> > self.res = RAIIFileAccess("a")
> >
> > class B():
> > def __init__(self):
> > self.res = RAIIFileAccess("b")
> >
> > class C():
> > def __init__(self):
> > self.a = A()
> > self.b = B()
> >
> > def main():
> > c = C()
>
> Looking at that code, my major thought is that there is far too much OO
> design, not enough simplicity.
If this is far too much OO for you then RAII will be of no
interest to you.
This example was specifically in response to a request to
illustrate the relative simplicity of RAII in the case of a
composite (OO) resource.
> Perhaps I'm missing something, but I have no idea what benefit there is
> in that style of code over:
>
> with open('a') as a:
> with open('b') as b:
> process(a, b)
Encapsulation. Your application code is now managing details
that should be hidden in the object. This PEP and RAII are
unashamedly targeted at OO designs.
If you would like to have a shot at coding this without RAII,
but preserving the OO design, you will find that it is
considerably _simpler_ than the with/context manager approach.
> So long as you only process a or b inside the nested block, you are
> guaranteed that they will be open.
>
> And unlike your RAII example, they will be closed when you exit,
> regardless of how many references to them you have, regardless of whether
> an exception occurs or not, regardless of whether there are cycles or
> whether they are globals or whether the interpreter is shutting down.
If you choose RAII you will not be cavalier with your references.
> I think that at this point, you have convinced me that you want to impose
> enormous costs on all Python interpreters *and* Python developers, in
> order to allow you to write C++ code in Python rather than learn Pythonic
> idioms like the with statement.
On interpreters yes. On developers no. You can carry on exactly as you are.
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