মাদার তেরেসা কোন দেশে জন্মগ্রহণ করেন?

Question:

What will be the output of the following Python code?

def extend_list(val, list=[]):
    list.append(val)
    return list

list1 = extend_list(10)
list2 = extend_list(123, [])
list3 = extend_list('a')

print(list1)
print(list2)
print(list3)

Options:

    
• A)
          [10]
        [123]
        ['a']     
    
• B)
          [10, 'a']
        [123]
        [10, 'a']     
    
• C)
          [10]
        [123]
        [10, 'a']     
    
• D)
          [10, 123, 'a']
        [10, 123, 'a']
        [10, 123, 'a']     

Correct Answer: Option B

Explanation:

In Python, default arguments are evaluated once when the function is defined, not each time the function is called. Because list=[] creates a single mutable list instance at definition time, that same list object will be used across all calls that do not provide an explicit list argument.

    
• Call 1 (list1 = extend_list(10)): The default empty list is modified to [10], and a reference to it is bound to list1.
    
• Call 2 (list2 = extend_list(123, [])): An explicit, new list is passed as the argument, so the default list is untouched. list2 becomes [123].
    
• Call 3 (list3 = extend_list('a')): The default list (which already contains [10]) is used again. 'a' is appended to it, making it [10, 'a']. Both list1 and list3 reference this exact same list.

Therefore, printing list1, list2, and list3 outputs [10, 'a'], [123], and [10, 'a'] respectively.