On 28.05.20 17:44, Christopher Barker wrote:
On Thu, May 28, 2020 at 3:50 AM Alex Hall <alex.moj...@gmail.com <mailto:alex.moj...@gmail.com>> wrote:On Thu, May 28, 2020 at 12:38 PM Greg Ewing <greg.ew...@canterbury.ac.nz <mailto:greg.ew...@canterbury.ac.nz>> wrote: But I'm having trouble thinking of one. I can't remember ever writing a function with a default argument value that *has* to be mutable and *has* to have a new one created on each call *unless* the caller provided one. Actually, we need to one further: a default argument value that *has* to be mutable and *has* to have a new one created on each call *unless* the caller provided one ... and *has* to treat None as valid value.
That's the scenario where you'd need to create a sentinel object to take the role of None. However late binding of defaults won't save you from this. The biggest advantage, as far as I understood, is that you can specify a default (expression) as part of the function header and hence provide a meaningful example value to the users rather than just None.
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