I don't remember if there's such function (I'm a bit rusty), but it can be done in two lines, using a for-loop.
This shows how, using the interpreter:
Code:
>>> the_string = "Hello, World!"
>>> the_list = []
>>> for each_character in the_string:
the_list.append(each_character)
>>> the_list
['H', 'e', 'l', 'l', 'o', ',', ' ', 'W', 'o', 'r', 'l', 'd', '!']
>>>