More on lists

This section covers some more operations on lists. See lists for an introduction to lists.

Removing values from a list

Another common operation on lists, is finding and removing values.

Removing values by index

The pop method of a list, removes a value at a given position in the list, and returns that value.

my_list = [9, 10, 3, 0]
my_list

[9, 10, 3, 0]

By default, with no arguments, it removes and returns the last value in the list:

last_value = my_list.pop()
last_value

0

The list has lost the last value.

my_list

[9, 10, 3]

You can give pop an argument, which is the position from which you want to get the value. pop removes the element at that position, shortening the list by one element.

mid_value = my_list.pop(1)
mid_value

10

my_list

[9, 3]

Removing values by finding

Sometimes we want to remove a certain specific value from the list.

For example, let’s say I have this list:

my_list = [9, 10, 999, 0]

I realize that I don’t want the 999 value. I can remove it, using the remove method of the list:

my_list.remove(999)

This modifies my list:

my_list

[9, 10, 0]

What happens if I have more than one value that matches my argument to remove?

my_list = [9, 10, 999, 0, 999]
my_list.remove(999)

We lost the first value that matches:

my_list

[9, 10, 0, 999]

Counting number of occurrences in a list

The count method of the list counts the number of occurrences of a particular value. The argument to the count method is the value you want to check for.

my_list = [9, 10, 999, 0, 999]
my_list.count(999)

2

Now we remove one of the 999 values, and count again:

my_list.remove(999)
my_list

[9, 10, 0, 999]

my_list.count(999)

1