Why no warnings when re-assigning builtin names?

Philip Semanchuk philip at semanchuk.com
Mon Aug 15 18:13:02 EDT 2011

On Aug 15, 2011, at 5:52 PM, Gerrat Rickert wrote:

> With surprising regularity, I see program postings (eg. on
> StackOverflow) from inexperienced Python users  accidentally
> re-assigning built-in names.
> For example, they'll innocently call some variable, "list", and assign a
> list of items to it.
> ...and if they're _unlucky_ enough, their program may actually work
> (encouraging them to re-use this name in other programs).

Or they'll assign a class instance to 'object', only to cause weird errors later when they use it as a base class.

I agree that this is a problem. The folks on my project who are new-ish to Python overwrite builtins fairly often. Since there's never been any consequence other than my my vague warnings that something bad might happen as a result, it's difficult for them to develop good habits in this regard. It doesn't help that Eclipse (their editor of choice) doesn't seem to provide a way of coloring builtins differently. (That's what I'm told, anyway. I don't use it.)

> If they try to use an actual keyword, both the interpreter and compiler
> are helpful enough to give them a syntax error, but I think the builtins
> should be "pseudo-reserved", and a user should explicitly have to do
> something *extra* to not receive a warning.

Unfortunately you're suggesting a change to the language which could break existing code. I could see a use for "from __future__ import squawk_if_i_reassign_a_builtin" or something like that, but the current default behavior has to remain as it is.


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