9.7. Deleting elements

There are several ways to delete elements from a list. If you know the index of the element you want, you can use pop:

t = ['a', 'b', 'c'] x = t.pop(1) print(t) print(x)

pop modifies the list and returns the element that was removed. If you don’t provide an index, it deletes and returns the last element.

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

alist = [4, 2, 8, 6, 5]
temp = alist.pop(2)
temp = alist.pop()
print(alist)

• [4, 8, 6]
• pop(2) removes the item at index 2, not the 2 itself.
• [2, 6, 5]
• pop() removes the last item, not the first.
• [4, 2, 6]
• Yes, first the 8 was removed, then the last item, which was 5.

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

alist = [4, 2, 8, 6, 5]
alist = alist.pop(0)
print(alist)

• [2, 8, 6, 5]
• alist is now the value that was returned from pop(0).
• [4, 2, 8, 6, 5]
• pop(0) changes the list by removing the first item.
• 4
• Yes, first the 4 was removed from the list, then returned and assigned to alist. The list is lost.
• None
• pop(0) returns the first item in the list so alist has now been changed.

If you don’t need the removed value, you can use the del operator:

t = ['a', 'b', 'c'] del t[1] print(t)

If you know the element you want to remove (but not the index), you can use remove:

t = ['a', 'b', 'c'] t.remove('b') print(t)

The return value from remove is None.

To remove more than one element, you can use del with a slice index:

t = ['a', 'b', 'c', 'd', 'e', 'f'] del t[1:5] print(t)

As usual, the slice selects all the elements up to, but not including, the second index.

Q-7: What is the value of alist after the following code executes?

alist = ['a', 'b', 'c', 'd', 'e', 'f']
del alist[1:5]
print(alist)

• ['a', 'b', 'c', 'd', 'e', 'f']
• The del method removes part of the list, so it will be shorter.
• ['a', 'f']
• 'a' is the 0th element of the list and 'f' is the 5th element of the list, so these are the values that remain after deleting [1:5].
• ['f']
• Remember that lists start at 0, not 1, and that a slice stops before the second element - not after.
• ['b', 'c', 'd', 'e']
• These are the values that will be deleted with the slice [1:5]

Q-8: Match each deletion method with its function. How does each operator and method work?
• del
• Gets rid of an element.
• pop
• Modifies a list and returns the removed element.
• del with a slice
• Gets rid of more than one element.
• remove
• Gets rid of an element without using the index.

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