List replication operator

[Steven D'Aprano]

On Fri, 25 May 2018 09:58:19 -0700, Rob Gaddi wrote:

[...]
>> This is a frequent, recurring pain point. Experienced programmers
>> forget how confusing the behaviour of * is because they're so used to
>> the execution model. They forget that writing a list comp is not even
>> close to obvious, not only for beginners but even some experienced
>> Python programmers.
>> 
>> 
> I agree that it's non-obvious, but I disagree with your diagnosis.  The
> non-obvious bit is that the empty list is a reference to a newly created
> mutable, not an immutable constant.  Or, more the point, that the word
> "mutable" is one that you need to know and think about in the first
> place.

I challenge you to read this bug report and claim that the poster's error 
was to *correctly* think that [[]]*5 made five references to the same 
list, but *incorrectly* failed to realise that list.append modified the 
list in place.

https://bugs.python.org/issue33636


> class list(_list):
>    @staticmethod
>    def replicate(*n, fill=_nodefault, call=list):
>      """Return a list of specified dimensions.
[...]

Interesting implementation to play with, thanks.



-- 
Steve