[Tutor] Output reason

[Richard Damon]

If I remember how that works right, there is a single empty list that is created and used for all the calls that use the default argument, and then your function modifies that empty list so it is no longer empty, and that modified list is used on future calls. (Not good to use a mutable as a default parameter).

A better solution would be to make the default something like None, and test if at the beginning of the function li is None, and if so set it to an empty list, and that empty list will be in function scope so it goes away and a new one is created on a new call.

> On Jul 12, 2019, at 10:24 AM, Gursimran Maken <gursimran.maken at gmail.com> wrote:
> 
> Hi,
> 
> Can someone please explain me the reason for below output.
> 
> Program:
> def fun(n,li = []):
>    a = list(range(5))
>    li.append(a)
>    print(li)
> 
> fun(4)
> fun(5,[7,8,9])
> fun(4,[7,8,9])
> fun(5) # reason for output (why am I getting to values in this output.)
> 
> Output:
> [[0, 1, 2, 3, 4]]
> [7, 8, 9, [0, 1, 2, 3, 4]]
> [7, 8, 9, [0, 1, 2, 3, 4]]
> [[0, 1, 2, 3, 4], [0, 1, 2, 3, 4]]
> 
> Thank you,
> Gursimran
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
> To unsubscribe or change subscription options:
> https://mail.python.org/mailman/listinfo/tutor