Python Coding Challange - Question With Answer

 

What will the following code output?

a = [1, 2, 3]
b = a.copy()
a[1:2] = [4, 5]
print(a, b)

(a) [1, 4, 5, 3] [1, 2, 3]
(b) [1, 4, 5, 3] [1, 4, 5, 3]
(c) [1, 2, 3] [4, 5]
(d) Error

Step-by-Step Explanation:

1. a = [1, 2, 3]
   • A list a is created with the elements [1, 2, 3].
2. b = a.copy()
   • The copy() method creates a shallow copy of the list a and assigns it to b.
   • b now contains [1, 2, 3] and is a separate object in memory from a. Any changes to a will not affect b.
3. a[1:2] = [4, 5]
   • This line modifies the list a using slice assignment:
     • The slice a[1:2] refers to the element(s) in index 1, which is [2] in this case.
     • The slice [2] is replaced with the elements [4, 5].
     • After this operation, a becomes [1, 4, 5, 3].
4. print(a, b)
   • a: The original list a has been modified to [1, 4, 5, 3] due to the slice assignment.
   • b: The shallow copy b remains unchanged, so it is still [1, 2, 3].

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Key Concepts:

1. Shallow Copy (copy()):

   • The copy() method creates a new, independent list. Changes to the original list do not affect the copy.

2. Slice Assignment:

   • The syntax a[start:end] = new_values replaces the elements in the specified range [start:end] with the elements in new_values.
   • In this case:
     • a[1:2] refers to the sublist [2] (element at index 1).
     • Replacing it with [4, 5] results in a = [1, 4, 5, 3].

3. List Expansion/Contraction:

   • Slice assignment can expand or shrink the list. For example:
     • If you replace a[1:2] with [4, 5, 6], the list will grow.
     • If you replace a[1:2] with [], the list will shrink.

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Visual Breakdown:

Step	List a	List b
Initial state	[1, 2, 3]	[1, 2, 3]
After copy	[1, 2, 3]	[1, 2, 3]
After assignment	[1, 4, 5, 3]	[1, 2, 3]