’দ্বৈত শাসন’ ব্যবস্থার প্রবর্তক কে?

Question:

Consider the following Python code snippet:

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

list_a = append_to(10)
list_b = append_to(20)

print(list_b)

What will be the output of executing this code?

Options:

    
• A) [20]
    
• B) [10, 20]
    
• C) [10]
    
• D) TypeError: default argument modified
  

Correct Answer: B) [10, 20]

Explanation:

In Python, default parameter values are evaluated only once when the function definition is executed, not each time the function is invoked.

    
• Because the default value target_list=[] is a mutable list, the same list instance is reused across subsequent function calls that do not provide an explicit argument for that parameter.
    
• During the first call append_to(10), the number 10 is appended to the default list, resulting in [10].
    
• During the second call append_to(20), the value 20 is appended to the same persistent list, resulting in [10, 20].
  

To avoid this behavior, it is standard practice to set the default argument to None and initialize a new list inside the function body when needed.