9.4. List Methods¶

As with strings, Python provides us with useful methods for lists. These methods will either change an existing list, return information about the list, or create and return a new list.

9.4.1. Common List Methods¶

Here is a sample of the most frequently used list methods. More complete lists can be found here:

To see detailed examples for a particular method, click on its name.

Methods That Return Information About The List¶
Method	Syntax	Description
count	`list_name.count(value)`	Returns the number of elements in the list that match `value`.
index	`list_name.index(value)`	Returns the index of the FIRST occurrence of `value` in the list. If the value is not in the list, Python throws an error.

Methods That Rearrange The Entries In The list¶
Method	Syntax	Description
reverse	`list_name.reverse()`	Reverses the order of the elements in a list.
sort	`list_name.sort()`	Arranges the elements of a list into increasing or decreasing order.

Methods That Add Or Remove Entries From A List¶
Method	Syntax	Description
append	`list_name.append(value)`	Adds `value` to the end of the list.
clear	`list_name.clear()`	Removes all elements from a list.
insert	`list_name.insert(index, value)`	Adds `value` at the specified `index` in the list. This pushes existing elements further down the list.
pop	`list_name.pop(index)`	Removes and returns the element at the given `index` value. If no `index` is provided, the last element in the list gets removed.
remove	`list_name.remove(value)`	Removes the FIRST element in a list that matches `value`.

Methods That Create New Lists¶
Method	Syntax	Description
join	`'connecter'.join(list_name)`	Combines all the elements of a list into a string.
split	`'string'.split('delimiter')`	Divides a string into smaller pieces, which are stored as separate elements in a new list.
list	`list(collection)`	This is a function rather than a method, and it behaves similarly to data conversion functions like `int()` and `str()`. The `list()` function tries to convert the whatever is inside the `()` into a list.

9.4.2. Check Your Understanding¶

As you answer these questions, follow the links in the table above as needed.

Question

What is printed by the following code?

string_list = ['coder', 'Tech', '47', '23', '350']
string_list.sort()
print(string_list)

[‘350’, ‘23’, ‘47’, ‘Tech’, ‘coder’]
[‘coder’, ‘Tech’, ‘23’, ‘47’, ‘350’]
[‘23’, ‘47’, ‘350’, ‘coder’, ‘Tech’]
[‘23’, ‘350’, ‘47’, ‘Tech’, ‘coder’]

Question

Which statement converts the string text = 'Coding students rock!' into the list ['Coding', 'students', 'rock!']?

text.join()
text.split()
text.join("")
text.split("")
list(text)

Question

What is printed by the following program?

grocery_bag = ['bananas', 'apples', 'edamame', 'chips', 'cucumbers', 'milk', 'cheese']
selected_items = []

selected_items = grocery_bag[2:5]
selected_items.sort()
print(selected_items)

[‘chips’, ‘cucumbers’, ‘edamame’]
[‘chips’, ‘cucumbers’, ‘edamame’, ‘milk’]
[‘apples’, ‘chips’, ‘edamame’]
[‘apples’, ‘chips’, ‘cucumbers’, ‘edamame’]

Question

What is printed by the following program?

a_list = [4, 2, 8, 6, 5]
a_list.append(True)
a_list.append(False)
print(a_list)

[4, 2, 8, 6, 5, False, True]
[4, 2, 8, 6, 5, True, False]
[True, False, 4, 2, 8, 6, 5]

Question

What is printed by the following program?

a_list = [4, 2, 8, 6, 5]
a_list.insert(2, True)
a_list.insert(0, False)
print(a_list)

[False, 4, 2, True, 8, 6, 5]
[4, False, True, 2, 8, 6, 5]
[False, 2, True, 6, 5]

Question

What is printed by the following program?

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

[4, 8, 6]
[2, 6, 5]
[4, 2, 6]