Python Coding Challange - Question With Answer(01181224)

What will the following Python code output? 

What will the following Python code output?

arr = [1, 3, 5, 7, 9]
res = arr[::-1][::2]
print(res)

Options:
[9, 7, 5, 3, 1]
[9, 5, 1]
[1, 5, 9]
[3, 7, 9]

Answer : 

Step 1: Understanding arr[::-1]

The slicing syntax [::-1] reverses the array.

• Original array: [1, 3, 5, 7, 9]
• Reversed array: [9, 7, 5, 3, 1]

So after the first slice (arr[::-1]), the array becomes:
[9, 7, 5, 3, 1]

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Step 2: Understanding [::2]

Now, we take the reversed array and apply the slicing [::2].

The slicing [::2] means:

• Start from the beginning of the array.
• Take every second element (step size = 2).

For the reversed array [9, 7, 5, 3, 1]:

• First element: 9 (index 0)
• Skip one element (7) and take 5 (index 2).
• Skip one more element (3) and take 1 (index 4).

Result after [::2]: [9, 5, 1]

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Step 3: Storing the Result in res

The final result of the combined slicing is stored in res:
res = [9, 5, 1]

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Step 4: Printing the Result

When you print res, the output is:

[9, 5, 1]

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Key Points:

1. [::-1] reverses the array.
2. [::2] selects every second element from the reversed array.
3. Combining slices gives the desired result [9, 5, 1].