[Python-ideas] revisit pep 377: good use case?
ironfroggy at gmail.com
Wed Feb 29 23:23:05 CET 2012
On Feb 29, 2012 4:56 PM, "Ethan Furman" <ethan at stoneleaf.us> wrote:
> 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.
I like the general idea, but a conditionally conditional control syntax is
a readability nightmare., however, I wonder if the case in which the with
statement act as a conditional could be explicit so a reader can
distinguish between those that will always execute their body and those
which may or may not.
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