Lesson 05-01: Python Lists¶

Data Type of Multiple Values¶

So far, each variable can only hold one value at a time - one integer or one float or one string. What if we wanted to hold multiple values? Like a list of prime numbers under 50? Or a list of names of students?

You can do this in python by creating a list! A list is a python datatype that can hold multiple values and has special functions, like a String. Here’s how you create a list:

numbers = [1,2,3,4,5,6]
names = ["Sally","Harry"]

Notice that it’s similar to a variable assignment statement, except the value uses square brackets ([]), and each value is separated by a comma (,).

Note that lists can hold values of different datatypes!

mixed_list = [1,2,"three",4,"5",true,None]

So once we have a list of values, how do we access them again?

Specific Elements in a List¶

Funnily enough, we do it exactly the same as we access strings! Just like each character in a string, each element in a list has an index and we use that index to access that value.

Here’s an example:

fruits = ["apple","banana","strawberry","grape","pineapple","watermelon"]

print(fruits) #entire list

print(fruits[0]) #apple

print(fruits[3]) #grape

print(fruits[-1]) #watermelon

​

['apple', 'banana', 'strawberry', 'grape', 'pineapple', 'watermelon']
apple
grape
watermelon

(ex_0501_1)

Notice how when the list is printed, it prints the entire list, including the brackets and quotes (if it’s a string).

List Slicing¶

Similar to strings, you can also slice lists using the same notation.

numbers = [0,1,2,3,4,5,6,7,8,9]

print(numbers)

print(numbers[0:3]) #0,1,2

print(numbers[5:8]) #5,6,7

print(numbers[-5:]) #5,6,7,8,9

print(numbers[4:5]) #4

​

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[0, 1, 2]
[5, 6, 7]
[5, 6, 7, 8, 9]
[4]

(ex_0501_2)

An important note - please see that in our last example, printing numbers[4:5] returned a list with the value in the 4th index. This is not the same as printing numbers[4]!

numbers = [0,1,2,3,4,5,6,7,8,9]

​

#list slice

print(numbers[4:5])

​

#list index

print(numbers[4])

​

#are they equivalent?

print(numbers[4] == numbers[4:5])

​

[4]
4
False

(ex_0501_3)

numbers[4:5] returns a list with the value at the 4th index. numbers[4] just returns the value at the 4th index.

We won’t be using list indexing as much in this course, but it was an interesting tidbit to share.

Checks For Understanding¶

#complete line 3 to return the 1st element in the given list a_list

def getFirstElement(a_list):

    return

​

​

#complete line 3 to return the last element in the given list a_list

def getFirstElement(a_list):

    return

​

​