বাংলায় দ্বৈতশাসন (Diarchy) কে প্রবর্তন করেন?

Question: What will be the output of the following Python code snippet?

def append_to(element, target=[]):
    target.append(element)
    return target

my_list = append_to(1)
print(append_to(2))

Options:

    
• A) [2]
    
• B) [1, 2]
    
• C) [[1], 2]
    
• D) TypeError: list indices must be integers

Correct Answer: B) [1, 2]

Explanation:

In Python, default argument values are evaluated only once at the time of function definition, rather than each time the function is invoked. Because a list is a mutable object, modifying it inside the function persists changes across successive calls that rely on the default value.

    
• First Call (append_to(1)): No second argument is passed, so Python assigns the default empty list to target. The integer 1 is appended, altering the default list to [1].
    
• Second Call (append_to(2)): Again, no second argument is provided, so the existing default list (now containing [1]) is reused. Appending 2 results in [1, 2], which is then returned and printed.

Best Practice: To avoid retaining mutated state between function calls, use None as a sentinel default value and initialize a new list inside the function:

def append_to(element, target=None):
    if target is None:
        target = []
    target.append(element)
    return target