Christian Heimes wrote: > Steven D'Aprano wrote: >> I suggest that Python should raise warnings.RuntimeWarning (or similar?) >> when a function is defined with a default argument consisting of a list, >> dict or set. (This is not meant as an exhaustive list of all possible >> mutable types, but as the most common ones that I expect will trip up >> newbies.) The warning should refer to the relevant FAQ or section in the >> docs. >> >> What do people think?
-0 from me. I'd rather feature it more prominently in the tutorial, a section "The five most common pitfalls" or something like that. > I don't see a chance for your proposal. How are you going to detect > mutable objects? Custom types can be mutable as well as immutable. A check at compilation time for list literals would catch 90 % of the cases. The warning would be targeted at newbies after all. It might still be a source of confusion when they try to import someone else's code that uses mutable defaults intentionally. Peter -- http://mail.python.org/mailman/listinfo/python-list
