Why no warnings when re-assigning builtin names?

Philip Semanchuk philip at semanchuk.com
Tue Aug 16 17:38:57 CEST 2011

On Aug 16, 2011, at 11:41 AM, Ethan Furman wrote:

> Philip Semanchuk wrote:
>> On Aug 16, 2011, at 1:15 AM, Steven D'Aprano wrote:
>>> Protecting n00bs from their own errors is an admirable aim, but have you
>>> considered that warnings for something which may be harmless could do more
>>> harm than good?
>> Isn't the whole point of a warning to highlight behavior that's not strictly
> > wrong but looks iffy? Sort of, "I can't be sure, but this looks like trouble
> > to me. I hope you know what you're doing". If we are to eschew warnings in
> > cases where they might be highlighting something harmless, then we would
> > have no warnings at all.
> Sounds good to me.  ;)  Keep such things in the IDE's, and then those who desire such behavior can have it there.  Do not clutter Python with such.

You wink, yet you sound serious. What's with the mixed message? Do you honestly advocate removing all warnings from Python, or not? I sincerely would like to know what you think.

>>> Perhaps. But I'm not so sure it is worth the cost of extra code to detect
>>> shadowing and raise a warning. After all, the average coder probably never
>>> shadows anything,
>> One need look no further than the standard library to see a strong
> > counterexample. grep through the Python source for " file =". I see dozens
>> of examples of this builtin being used as a common variable name. I would
> > call contributors to the standard library above-average coders, and we can
> > see them unintentionally shadowing builtins many times.
> What makes you think it's unintentional?  file makes a good variable name, and if you don't need it to actually open a file there's nothing wrong with using it yourself.

"Unintentional" as in, "I'm using file as a variable name because it's handy" as opposed to intentional as in "Yes, I am deliberately changing the meaning of this builtin". 

>>> and for those that do, once they get bitten *once* they
>>> either never do it again or learn how to shadow safely.
>> I have done it plenty of times, never been bitten (thankfully) and still
> > do it by accident now and again.
> Seems to me the real issue is somebody using a builtin, such as str or int, and that they somehow manage to do this without realizing, "wait a sec', that's one of my variables!"  


> I don't see that as a problem that Python needs to solve.

"need" is a strong word. Python will be fine regardless of whether this changes or not. I believe Python could be improved; that's all I'm arguing.


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