[Python-Dev] anonymous blocks
sabbey at u.washington.edu
Tue Apr 19 21:55:33 CEST 2005
Guido van Rossum wrote:
>> See the thread "pre-PEP: Suite-Based Keywords" (shamless plug)
>> (an earlier, similar proposal is here:
>> %40python.org ).
>> In short, if doFoo is defined like:
>> def doFoo(func1, func2):
>> You would be able to call it like:
>> def func1(a, b):
>> return a + b
>> def func2(c, d):
>> return c + d
>> That is, a suite can be used to define keyword arguments.
> I'm still not sure how this is particularly solving a pressing problem
> that isn't solved by putting the function definitions in front of the
> call. I saw the first version of the proto-PEP and didn't think that
> the motivating example (keeping the getx/setx methods passed to a
> property definition out of the class namespace) was all that valuable.
OK. I think most people (myself included) who would prefer to define
properties (and event handlers, etc.) in this way are motivated by the
perception that the current method is just ugly. I don't know that it
solves any pressing problems.
> Two more issues:
> (1) It seems that *every* name introduced in the block automatically
> becomes a keyword argument. This looks like a problem, since you could
> easily need temporary variables there. (I don't see that a problem
> with class bodies because the typical use there is only method and
> property definitions and the occasional instance variable default.)
Combining the suite-based keywords proposal with the earlier, 'where'
proposal (linked in my above post), you would be able to name variables
individually in the case that temporary variables are needed:
x = [i**2 for i in [1,2,3]]
> (2) This seems to be attaching a block to a specific function call but
> there are more general cases: e.g. you might want to assign the return
> value of doFoo() to a variable, or you might want to pass it as an
> argument to another call.
The 'where' proposal also doesn't have this problem. Any expression is
> *If* we're going to create syntax for anonymous blocks, I think the
> primary use case ought to be cleanup operations to replace try/finally
> blocks for locking and similar things. I'd love to have syntactical
> support so I can write
> instead of
Well, that was my other proposal, "pre-PEP: Simple Thunks" (there is also
an implementation). It didn't seem to go over all that well. I am going
to try to rewrite it and give more motivation and explanation (and maybe
use 'with' and 'from' instead of 'do' and 'in' as keywords).
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