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9.5. List slices

The slice operator also works on lists:

t = ['a', 'b', 'c', 'd', 'e', 'f'] print(t[1:3]) print(t[:4]) print(t[3:])

If you omit the first index, the slice starts at the beginning. If you omit the second, the slice goes to the end. So if you omit both, the slice is a copy of the whole list.

>>> t[:]
['a', 'b', 'c', 'd', 'e', 'f']

Q-2: What is printed by the following statements?

alist = [3, 67, "cat", [56, 57, "dog"], [ ], 3.14, False]
print(alist[4:])

• [ [ ], 3.14, False]
• Yes, the slice starts at index 4 and goes up to and including the last item.
• [ [ ], 3.14]
• By leaving out the upper bound on the slice, we go up to and including the last item.
• [ [56, 57, "dog"], [ ], 3.14, False]
• Index values start at 0.

Q-3: What is printed by the following statements?

alist = [3, 67, "cat", [56, 57, "dog"], [ ], 3.14, False]
print(alist[:])

• []
• An empty slice like this would not produce an empty list. Think about how the slice indexes.
• [3]
• This would be correct if the slice was [:1]
• [3, 67, "cat", [56, 57, "dog"], [ ], 3.14, False]
• Omitting both indexes in a slice will create a copy of the whole list.

Since lists are mutable, it is often useful to make a copy before performing operations that fold, spindle, or mutilate lists.

A slice operator on the left side of an assignment can update multiple elements:

t = ['a', 'b', 'c', 'd', 'e', 'f'] t[1:3] = ['x', 'y'] print(t)

Q-5: What is printed by the following statements?

L = [0.34, '6', 'SI106', 'Python', -2]
print(len(L[1:-1]))

• 2
• The list begins with the second item of L and includes everything up to but not including the last item.
• 3
• Yes, there are 3 items in this slice.
• 4
• The list begins with the second item of L and includes everything up to but not including the last item.
• 5
• The list begins with the second item of L and includes everything up to but not including the last item.

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