break up a value in a list to a list of individual items

[r3bol]

Hi, sorry to post this, but I've had a really hard time finding how to
do it.
Q.
How can I break up a value in a list to a list of individual items
(preferably without importing any modules)?
Like...
['12345'] (string)
to
[1, 2, 3, 4, 5] [numbers]

Thanks.