H a n d s o n, p r o j e c t b a s e d

Modifying Elements in a List
The syntax for modifying an element is similar to the syntax for accessing 
an element in a list. To change an element, use the name of the list followed 
by the index of the element you want to change, and then provide the new 
value you want that item to have.

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Introducing Lists
37
For example, let’s say we have a list of motorcycles, and the first item in 
the list is 
'honda'
. How would we change the value of this first item?
 motorcycles.py u motorcycles = ['honda', 'yamaha', 'suzuki']
print(motorcycles)
v
motorcycles[0] = 'ducati'
print(motorcycles)
The code at u defines the original list, with 
'honda'
as the first element. 
The code at v changes the value of the first item to 
'ducati'
. The output 
shows that the first item has indeed been changed, and the rest of the list 
stays the same:
['honda', 'yamaha', 'suzuki']
['ducati', 'yamaha', 'suzuki']
You can change the value of any item in a list, not just the first item.
Adding Elements to a List
You might want to add a new element to a list for many reasons. For 
example, you might want to make new aliens appear in a game, add new 
data to a visualization, or add new registered users to a website you’ve 
built. Python provides several ways to add new data to existing lists.
Appending Elements to the End of a List
The simplest way to add a new element to a list is to append the item to the 
list. When you append an item to a list, the new element is added to the end 
of the list. Using the same list we had in the previous example, we’ll add the 
new element 
'ducati'
to the end of the list:
motorcycles = ['honda', 'yamaha', 'suzuki']
print(motorcycles)
u
motorcycles.append('ducati')
print(motorcycles)
The 
append()
method at u adds 
'ducati'
to the end of the list without 
affecting any of the other elements in the list:
['honda', 'yamaha', 'suzuki']
['honda', 'yamaha', 'suzuki', 'ducati']

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38
Chapter 3
The 
append()
method makes it easy to build lists dynamically. For 
example, you can start with an empty list and then add items to the list 
using a series of 
append()
calls. Using an empty list, let’s add the elements 
'honda'
, 
'yamaha'
, and 
'suzuki'
to the list:
motorcycles = [] 
motorcycles.append('honda') 
motorcycles.append('yamaha') 
motorcycles.append('suzuki') 
print(motorcycles)
The resulting list looks exactly the same as the lists in the previous 
examples:
['honda', 'yamaha', 'suzuki']
Building lists this way is very common, because you often won’t know 
the data your users want to store in a program until after the program is 
running. To put your users in control, start by defining an empty list that 
will hold the users’ values. Then append each new value provided to the list 
you just created.