Python · Lists
Analyse Lists
The full text of this chapter, to read or revisit. To practise, do the exercises.
▶ Do the exercisesExercise 1 — Analyzing Lists
Now that you know how to add and remove elements, let's learn how to analyze your lists! In this chapter, we'll explore four essential methods and functions for getting information about lists:
•
len()
- Get the number of items in a list
•
index()
- Find the position of a specific item
•
count()
- Count how many times an item appears
•
in
- Check if an item exists in a list
These tools are essential for understanding and working with your lists. Let's use our Codémon examples to see how they work!
Exercise 2 — The len() Function
The
len()
function returns the number of items in a list. It's very useful to check how many elements you have!
# Your Codémon team
my_team = ["Zap", "Aquachu", "Pyrochu"]
print("My team:", my_team)
print("My team size:", len(my_team))
print("-" * 40)
# Enemy team
enemy_team = ["Pyrochu"]
print("Enemy team:", enemy_team)
print("Enemy team size:", len(enemy_team))
print("-" * 40)
# Empty team (just started the game!)
empty_team = []
print("Empty team:", empty_team)
print("Empty team size:", len(empty_team))
len() works with many types!
The
len()
function can be used with other data types too, like strings, tuples, and dictionaries (you'll learn about those later). It's one of the most useful functions in Python!
Exercise 3 — Understanding len()
What will be the output of the following code?
codemons = ["Aquachu", "Pyrochu", "Florachu", "Rockachu"]
print(len(codemons))
Hint : The len() function counts the number of items in the list.
Exercise 4 — The index() Method
The
index()
method finds the position of an element in a list. It returns the index of the first occurrence of the element.
Basic syntax:
list.index(element, start, end)
-
element
: Required - the item to search for
-
start
: Optional - where to start the search (default is 0)
-
end
: Optional - where to end the search (default is the end of the list)
codemons = ['Aquachu', 'Pyrochu', 'Florachu', 'Aquachu', 'Pyrochu']
# Find the first occurrence of 'Aquachu'
first_aquachu = codemons.index('Aquachu')
print("First Aquachu is at index:", first_aquachu)
# Find 'Aquachu' starting from index 1
second_aquachu = codemons.index('Aquachu', 1)
print("Second Aquachu is at index:", second_aquachu)
# Find 'Pyrochu' between indices 2 and 5
second_pyrochu = codemons.index('Pyrochu', 2, 5)
print("Second Pyrochu is at index:", second_pyrochu)
What if the element is not found?
If the element is not found in the list, Python will raise a ValueError. It's a good practice to check if an element is in the list before using index() with the 'in' operator.
Exercise 5 — Using the index() Method
1. Find the position of the first "Pyrochu".
2. Find the position of the second "Aquachu" (after the first one).
team = ['Aquachu', 'Pyrochu', 'Florachu', 'Aquachu']
first_pyrochu = team.____('Pyrochu')
print("First Pyrochu position:", first_pyrochu)
second_aquachu = team.index('Aquachu', ____)
print("Second Aquachu position:", second_aquachu)
Options: index find position 1 0 5
Hint : Remember: The index() method returns the position of the first occurrence of an element. To find subsequent occurrences, use the start parameter to begin searching after the first occurrence.
Exercise 6 — The count() Method
The
count()
method returns the number of times a specified element appears in a list.
Basic syntax:
list.count(element)
-
element
: The item to count occurrences of
codemons = ['Aquachu', 'Pyrochu', 'Florachu', 'Aquachu', 'Pyrochu', 'Aquachu']
# Count how many Aquachu are in the team
aquachu_count = codemons.count('Aquachu')
print("Number of Aquachu:", aquachu_count)
# Count how many Florachu are in the team
florachu_count = codemons.count('Florachu')
print("Number of Florachu:", florachu_count)
# Count a Codémon that isn't in the team
test_count = codemons.count('Test')
print("Number of Test:", test_count) # Returns 0 instead of an error
Exercise 7 — Using the count() Method
What will be the output of the following code?
numbers = [1, 2, 3, 1, 0]
print(numbers.count(1) + numbers.count(0))
Hint : Remember: In Python, count() counts the occurrences of a specified value in a list.
Exercise 8 — The 'in' Operator for Lists
The
in
operator allows you to check if an item exists in a list. It returns
True
if the item is in the list, and
False
if it's not.
# A list of Codémon types
codemon_types = ["water", "fire", "grass", "electric"]
# Check if "fire" is in the list
print("fire" in codemon_types)
# Check if "rock" is in the list
print("rock" in codemon_types)
You can also use
not in
to check if an item is NOT in the list:
codemon_types = ["water", "fire", "grass", "electric"]
# Check if "rock" is not in the list
print("rock" not in codemon_types)
The 'in' operator is versatile
The
in
operator works with many Python sequences, not just lists. You can use it with strings, tuples, sets, and dictionaries.
Exercise 9 — Using the 'in' Operator
Given the following list, what will be the result of the expression?
codemon_collection = ["Aquachu", "Pyrochu", "Florachu"]
print("Pyrochu" in codemon_collection)
Options
• ```True```
• ```False```
• ```"Pyrochu"```
• ```1```
Hint : Remember: The ```in``` operator checks if an item exists in a list and returns a boolean value.
Exercise 10 — Checking for Codémon Types
1. Check if the desired Codémon type is available in your collection.
2. Check if the "rock" type is not in your collection.
available_types = ["water", "fire", "grass"]
desired_type = "fire"
# Check if the desired type is available
if desired_type ____ available_types:
print("You have this type!")
else:
print("You don't have this type.")
# Check if "rock" type is not in the collection
if "rock" ____ ____ available_types:
print("Rock type not found.")
Options: in = == not in !=
Hint : Remember: Use ```in``` to check if an element is in a list, and ```not in``` to check if it's not in the list.
Exercise 11 — Match Analysis Methods
Match each method or function with its correct description.
Items to match
• len(team)
• team.index('Aquachu')
• team.count('Pyrochu')
• team.index('Florachu', 2)
• 'Zap' in team
Definitions
• Returns the number of items in the list
• Finds the position of the first 'Aquachu'
• Counts how many 'Pyrochu' are in the list
• Finds 'Florachu' starting search from index 2
• Checks if 'Zap' exists in the list
Exercise 12 — Analyzing a Team
You need to analyze a Codémon team. Which code correctly:
1. Gets the total number of Codémon
2. Finds the position of 'Florachu'
3. Counts how many 'Aquachu' are in the team
4. Checks if 'Zap' is in the team
Options
• total = len(team)
position = team.index('Florachu')
count = team.count('Aquachu')
has_zap = 'Zap' in team
• total = team.size()
position = team.index('Florachu')
count = team.count('Aquachu')
has_zap = 'Zap' in team
• total = len(team)
position = team.find('Florachu')
count = team.count('Aquachu')
has_zap = team.has('Zap')
• total = team.length()
position = team.index('Florachu')
count = team.count('Aquachu')
has_zap = team.contains('Zap')
Hint : Remember: ```len()``` gets the size, ```index()``` finds the position, ```count()``` counts occurrences, and ```in``` checks membership.
Exercise 13 — Challenge - Team Statistics
You're a Codémon trainer and need to analyze your team!
Your tasks:
1. Count the total number of Codémon in your team
2. Find the position of "Florachu" in your team
3. Count how many "Aquachu" you have
4. Count how many "Pyrochu" you have
5. Check if "Zap" is in your team
Use
len()
,
index()
,
count()
, and
in
to complete this challenge!
Starter code
# Your Codémon team
my_team = ["Aquachu", "Pyrochu", "Florachu", "Aquachu", "Zap", "Pyrochu", "Aquachu"]
print("My team:", my_team)
print("=" * 50)
# Task 1: Count total Codémon
# Task 2: Find position of Florachu
# Task 3: Count Aquachu
# Task 4: Count Pyrochu
# Task 5: Check if Zap is in the team