What will be the output of the following Python code, and why?

The code will print:

[1]

[1, 2]

The function uses a mutable default argument (a list). The default list is created once when the function is defined, not each time it is called. Thus, the first call appends 1 to the shared list and returns [1]. The second call appends 2 to the same list, so the list now contains [1, 2]. This is a common Python pitfall. The correct pattern is to use None as the default and create a new list inside the function: def append_item(item, lst=None): if lst is None: lst = [] ...