কার মতে, শিল্পকলার আত্মার গভীর ধ্যান- ধারণার প্রতিচ্ছবি?

Question:

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

def append_to_list(value, target_list=[]):
    target_list.append(value)
    return target_list

print(append_to_list(1))
print(append_to_list(2))

Options:

    
• A) [1] followed by [2]
    
• B) [1] followed by [1, 2]
    
• C) [1, 2] followed by [1, 2]
    
• D) [1] followed by an error

Correct Answer: B) [1] followed by [1, 2]

Explanation:

In Python, default parameter values are evaluated once when the function is defined, not each time the function is invoked. Because a list is a mutable object, the same list instance is reused across multiple calls that do not provide an explicit argument for target_list.

    
• First Call: append_to_list(1) binds target_list to the default empty list, appends 1, and returns [1].
    
• Second Call: append_to_list(2) reuses the modified default list (which already holds [1]), appends 2, and returns [1, 2].

Best Practice Tip: To avoid unexpected behavior with mutable default arguments, use None as the default value and instantiate a new list within the function body:

def append_to_list(value, target_list=None):
    if target_list is None:
        target_list = []
    target_list.append(value)
    return target_list