Lists are one of the fundamental data types that we use in Python for solving real problems. Being able to manipulate lists and access items is necessary for effective programming. In this hands-on lab, we’ll be working through some exercises demonstrating that we understand how to add, remove, modify, and read items from lists in Python. We’ll perform actions on a list to meet some checkpoint requirements provided to us within a Python file.
To feel comfortable completing this lab we’ll want to know how to do the following:
* Working with list literals: Watch the “Lists” video from the Certified Entry-Level Python Programmer Certification course.
* Using list functions and methods: Watch the “List Functions and Methods” video from the Certified Entry-Level Python Programmer Certification course.
Learning Objectives
Successfully complete this lab by achieving the following learning objectives:
- Create a users List and Add Initial Items
Note: The
using-lists.pyfile exists in the /home/cloud_user/ directory. If you do not see the file, please give the lab another minute to finish provisioning. If you prefer to use your own local Python editor, you can also access the initialusing-lists.pyfile in the lab’s GitHub repository.Our first few tasks require us to create the
usersvariable that we’re going to work with throughout the lab and then add some information to it. Here’s how we complete the first task:using-lists.py (partial)
# 1) Set the users variable to be an empty list users = [] assert users == [], f"Expected `users` to be [] but got: {repr(users)}"Now if we run the file we should see the error for the second task:
$ python3.7 using-lists.py Traceback (most recent call last): File "./using-lists.py", line 8, in <module> assert users == ['kevin', 'bob', 'alice'], f"Expected `users` to be ['kevin', 'bob', 'alice'] but got: {repr(users)}" AssertionError: Expected `users` to be ['kevin', 'bob', 'alice'] but got: []This error shows us that we need to add values to the list before we can continue. The task also specifies that we shouldn’t just reassign the
usersvariable. Here’s an example solution to this:using-lists.py (partial)
# 2) Add 'kevin', 'bob', and 'alice' to the users list in that order without reassigning the variable. users.append('kevin') users.append('bob') users.append('alice') assert users == ['kevin', 'bob', 'alice'], f"Expected `users` to be ['kevin', 'bob', 'alice'] but got: {repr(users)}"- Remove bob and Create rev_users List
For tasks 3 and 4 we need to remove the
bobvalue and then create a new reversed version of the new list. Here’s an example solution for both of these tasks:using-lists.py (partial)
# 3) Remove 'bob' from the `users` list without reassigning the variable. del users[1] assert users == ['kevin', 'alice'], f"Expected `users` to be ['kevin', 'alice'] but got: {repr(users)}" # 4) Reverse the users list and assign the result to `rev_users` rev_users = list(reversed(users)) assert rev_users == ['alice', 'kevin'], f"Expected `rev_users` to be ['alice', 'kevin'] but got: {repr(rev_users)}"The
delstatement will allow us to remove an item at a specific index to complete task three. For task four, we’ll use thereversedfunction and then cast the result of that back to a list using thelistfunction.- Insert melody to users and Concatenate Lists
For tasks five and six we’ll be adding more information to our
userslist. To add a single item at the first index we’ll use theinsertmethod. To add three new items to the end of the list we’ll use list concatenation and reassign theusersvariable.using-lists.py (partial)
# 5) Add the user 'melody' to users where 'bob' used to be. users.insert(1, 'melody') assert users == ['kevin', 'melody', 'alice'], f"Expected `users` to be ['kevin', 'melody', 'alice'] but got: {repr(users)}" # 6) Add the users 'andy', 'wanda', and 'jim' to the users list using a single command users += ['andy', 'wanda', 'jim'] assert users == ['kevin', 'melody', 'alice', 'andy', 'wanda', 'jim'], f"Expected `users` to be ['kevin', 'melody', 'alice', 'andy', 'wanda', 'jim'] but got: {repr(users)}"- Slice`users to Return 3rd and 4th Elements
For the final task, we’ll extract a subsection from the
userslist to create the newcenter_userslist. We can extract the third and fourth items from the list by slicing from2to4.using-lists.py (partial)
# 7) Slice the users lists to return the 3rd and 4th items and assign the result to `center_users` center_users = users[2:4] assert center_users == ['alice', 'andy'], f"Expected `users` to be ['alice', 'andy'] but got: {repr(center_users)}"
