Python Coding Challange - Question with Answer (01060625)

 

General slicing syntax:

a[start:stop:step]

• start → where to begin (inclusive)

• stop → where to stop (exclusive)

• step → direction and spacing

  • If positive, slicing moves left to right

  • If negative, slicing moves right to left

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 Applying to your code:

a = [1, 2, 3, 4, 5, 6, 7]
print(a[1:6:-1])

• start = 1 → this is the element 2 (a[1])

• stop = 6 → this is the element 7 (a[6])

• step = -1 → go backwards

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 Important rule:

When step is negative, it slices backward. So Python expects:

start > stop

But here:

start = 1 

stop = 6

• 1 < 6 → invalid direction for -1 step

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✅ Result:

[]

No elements are returned because the step is -1, but the direction (from index 1 to 6) is invalid for backward slicing.

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✅ Summary:

a[1:6:-1] → []  
# Because step = -1 (backward), but start < stop, so nothing is selected.

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