To start this guide, download this zip file.
A list contains a collection of values. You have already seen variables that hold a single value:
number = 5
A variable that references a list can hold multiple values, in order:
names = ['Maria', 'Mariano', 'Anna', 'Antonino'] numbers = [5, 8, 10, 13, 42]
A list can hold as many values as you want. We can even have an empty list:
twilight_books_i_like = 
To get the length of a list, use
number_of_names = len(names)
number_of_names will be equal to 4.
Appending to a list
One of the many functions we can perform on a list is appending items to it. This means adding items to the end of the list. For example:
pets = ['cat', 'horse', 'dog'] pets.append('emu')
This will result in the pets list now containing
['cat', 'horse', 'dog', 'emu'].
Note the syntax here — variable dot function:
You can use input loops to start with an empty list and then add more items to
it. In the zip file you will find a small program in
illustrates how to do this:
if __name__ == '__main__': names =  while True: name = input("Give me a name: ") if name == 'q': break names.append(name) print(names)
We start with an empty list, using
names = .
We use the event stream pattern, looping forever and then breaking out of the loop if the person enters ‘q’ instead of a name. (Note, if you were making a program to enter characters in Star Trek, you might not want to do it this way.)
append()to add each name to the list.
If you run this program, you will see something like this:
Give me a name: me Give me a name: you Give me a name: everyone Give me a name: q ['me', 'you', 'everyone']
Once you have a list, you can iterate (or loop) through it using
for ... in:
for number in numbers: print(number)
Each time through the
for loop, Python sets the variable
number to one of
the numbers in the list, in order. Since we have set the
numbers variable to
[5, 8, 10, 13, 42], the first time through the loop,
number = 5. The second
time through the loop,
number = 8, and so forth. So this code will print:
5 8 10 13 42
The name of the variable can be whatever you like. For example:
for cute_puppies in numbers: print(cute_puppies)
However, you want to be sure that your friends can read your code and make sense of it!
Your code is much more readable if you use variables that make sense.