Lists

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We have seen numbers and strings as types.

>>> a = 10
>>> type(a)
<class 'int'>

>>> b = 1.0
>>> type(b)
<class 'float'>

>>> my_name = "Matthew"
>>> type(my_name)
<class 'str'>

Another useful type, is the list. Here we make an empty list:

>>> my_list = []
>>> type(my_list)
<class 'list'>

We can also put elements into the list:

>>> my_list = [2, 4, 6]
>>> my_list
[2, 4, 6]

What do you think you will get from len(my_list)?

Like other Python object, lists have methods. Methods are functions, attached to the object, that operate on the object. You can get to the methods with the variable name (e.g. my_list) followed by a dot ., followed by the method name. One useful method for a list is append. It works like this:

>>> another_list = []
>>> another_list
[]
>>> another_list.append(3)
>>> another_list
[3]
>>> another_list.append(5)
>>> another_list
[3, 5]

Another useful method is count. It counts the number of times a particular element occurs in the list.

>>> another_list.count(3)
1
>>> another_list.append(3)
>>> another_list.count(3)
2
>>> another_list.count(99)
0

Exercises:

Use a for loop to make a list of all the numbers between 0 and 10.

Use a for loop to make a list of all the numbers from 0 through 99 that are divisible by 3 and by 4.

Use a for loop and the randint function from the random module to make 100 random integers in the range 0 through 10. Count how many zeros you got.