[Python-ideas] revisit pep 377: good use case?
ethan at stoneleaf.us
Wed Feb 29 23:03:00 CET 2012
Craig Yoshioka wrote:
> On Feb 29, 2012, at 11:55 AM, Ethan Furman wrote:
>> From PEP 343:
>> But the final blow came when I read Raymond Chen's rant about
>> flow-control macros. Raymond argues convincingly that hiding
>> flow control in macros makes your code inscrutable, and I find
>> that his argument applies to Python as well as to C.
>> So it is explicitly stated that the with statement should not be
>> capable of controlling the flow.
> I read the rant, and I agree in principle, but I think it's also a far stretch to draw a line between a very confusing non-standard example of macros in C, and documentable behavior of a built-in statement. That is, the only reason you might say with would be hiding flow-control is because people don't currently expect it to. I also think that when people use non-builtin contextmanagers it's usually within a very specific... context (*dammit*), and so they are likely to look up why they are using an object as a context manager. That's where you would document the behavior:
> with uncached(path):
> # code here only executes if the path does not exist
I am -1 on the idea.
if / while / for / try are *always* flow control.
Your proposal would have 'with' sometimes being flow control, and
sometimes not, and the only way to know is look at the object's code
and/or docs. This makes for a lot more complication for very little gain.
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