Ever heard of sets in math? In programming, those are lists!

What are lists?

As we know, Python has variables. Variables can store one piece of data, no matter what data type that is. It can store numbers, strings, booleans, and now, lists. However a variable which carries a list carries multiple values with it, as lists (just like how the name implies) contain multiple elements. They are formed with square brackets and the elements they contain are seperated by commas.

x = ["A", "B", "C", 1, 2, 3, True, False]

An important aspect of lists is the fact that they are indexible. This means that all the elemenst of a list have an index number, so a number which specifies where they are in the list. Indexing starts at 0, so they first element of the list has an index number of 0.

x = ["A", "B", "C", 1, 2, 3, True]

one = x[0]

two = x[6]

print(one)

print(two)

Output: 

"A" # the first element of the list has an index number of 0

True # the seventh element of the list has an index number of 7

Just like how we can retrieve just one element from a list, we can retrieve many through slicing. First, we would write the list and then open square brackets. We'd first write where we want to start slicing, where we want to end (which doesn't include the element with that index number) and by how many steps we wish to proceed. The syntax is below:

list[start:end:step]

For example:

x = ["A", "B", "C", 1, 2, 3, True, False]

print(x[0:3])

print(x[0:4:2])

print(x[2:])

Output:

['A', 'B', 'C']

['A', 'C']

['C', 1, 2, 3, True, False]

Lists can be placed inside other lists and sliced accordingly:

our_list = [[1,2,3], [4,5,6], [7,8,9]]

print(our_list[1][2])

Output:

6

Lists can of course have elements added to them and removed from them. Removing an element from a list is as simple as using the .remove() method.

users = ["Alice", "Bob", "Charlie", "Dan"]

users.remove("Bob")

print(users)

Output:

users = ["Alice", "Charlie", "Dan"]

Another method for removing elements is by using the del keyword with an index number.

del users[0]

print(users)

Output:

users = ["Charlie", "Dan"]

As for adding elements to a list, there are several methods. The most popular method is using the .append() method, which adds a new element to the end of the list.

users.append("Noah")

print(users)

Output:

users = ["Charlie", "Dan", "Noah"]

Although this is a method used consistently to add new elements to lists, the following code includes some other common methods:

A = []

A = A + [1] # this adds 1 to the end of the list

A = A + ["BCD"]

print(A)

A = A + [5, 6, 7, 8] # adds all of the elements in here individually

print(A)

A = A + [[5, 6, 7, 8]] # adds [5, 6, 7, 8] as one element

print(A)

A.insert(2, 100) # inserts 100 as the second index item

print(A) # the five moves one space

A[0] = 2 # makes the 0 index as 2, gets rid of one

print(A)

Here is the official documentation made by Python regarding adding and removing items from lists.